A
abrasive discs (cutting wheels)
Abrasive wheels or flat discs fitted to bench, pedestal, and portable grinders.
abrasive disc
Abrasive wheels or flat discs fitted to bench, pedestal, and portable grinders.
ABS code retrieval key
A specially shaped metal key that is inserted into the data link connector to retrieve DTCs.
ABS pressure tester
A high-pressure gauge designed to connect to the HCU and used to measure high hydraulic pressures in the system.
ABS proportioning valve depressor
A tool used to hold the proportioning valve open on some ABS HCUs.
absorbed glass mat
A type of lead-acid battery.
acceleration
An increase in a vehicle’s speed.
accelerator pedal
The foot-operated pedal used by the driver to increase and decrease the amount of power the engine develops.
accelerator pump circuit
The carburetor circuit involved with heavy acceleration, directly connected to the accelerator pump. Also used to prime the engine during cold starting.
accelerator pump
A small pump usually located inside the carburetor that sprays an extra amount of fuel into the carburetor air horn during acceleration.
accelerometer
An electronic instrument that measures the amount of acceleration in a specific direction.
accelerometers
An electronic instrument that measures the amount of acceleration in a specific direction.
accessory drive pulleys
A round circular metal disc attached to the front of the engine crankshaft with a rubber/fiber belt that helps operate automotive accessories.
accessory drive pulley
A round circular metal disc attached to the front of the engine crankshaft with a rubber/fiber belt that helps operate automotive accessories.
accumulator (heating and cooling system)
A device placed between the evaporator and the compressor to collect liquid refrigerant and prevent it from entering the compressor.
accumulator (manual transmission)
A device used to reduce the speed of clutch or band application to help prevent harsh shifting.
accumulator (brakes)
A storage container that holds pressurized brake fluid.
Accumulator
The air-conditioning component used on fixed orifice systems to protect the compressor by storing liquid refrigerant, so it does not reach the compressor.
accumulators
A device used to reduce the speed of clutch or band application to help prevent harsh shifting.
Ackermann angle
The angle the steering arms make with the steering axis, projected toward the center of the rear axle.
Ackermann principle
The geometric alignment of linkages in a vehicle’s steering such that the wheels on the inside of a turn can move in a different circle radius than the wheels on the outside.
activated charcoal
Charcoal that will absorb large amounts of vapor, used in charcoal canisters to store and release fuel vapors.
active control
A system of providing constant feedback from sensors in the vehicle to the control unit.
actuating
The act of making something move or work.
actuator (heating and cooling system)
A device that is electrically or vacuum controlled and is used to physically move doors within the heater box to control airflow.
actuator (general)
A mechanical part usually controlled by electricity allowing a module to control something mechanical.
actuator
A mechanical part usually controlled by electricity allowing a module to control something mechanical.
actuators
A device that moves the air doors of the air box. It is controlled by input from the climate control panel.
adaptive air suspension
A suspension system that uses rubber bags or bladders filled with air to support the weight of the vehicle.
adjustable bushing
A brace or nylon part that pushes against the rack to adjust the mesh of the rack teeth to the pinion teeth.
adjusting nut
The nut used to adjust the end play or preload of a wheel bearing.
adjustment sleeve
A component that connects the tie-rods together and to the center link on some applications, providing the adjustment point for toe-in or toe-out, depending on the manufacturer’s specifications.
advance mechanism
A device used to trigger an earlier spark based on engine conditions.
aerate
The tendency to create air bubbles in a fluid.
after top dead center (ATDC)
The position of the piston once it has moved beyond top dead center.
aftermarket
That segment of the trade that supplies parts, services, and repair for vehicles outside of the original equipment manufacturer (OEM) or the dealer network.
air gap
The space or clearance between two components, such as the space between the tone wheel and the pick-up coil in a wheel speed sensor.
air checking
The use of compressed air to check clutch and servo operation on transmissions during and after assembly.
air diverter valve
A valve that changes secondary airflow from the exhaust stream to the air cleaner or vice versa.
air driers
A device fitted to compressed air lines to remove moisture.
air drill
A compressed air–powered drill.
air hammer
A tool powered by compressed air with various hammer, cutting, punching, or chisel attachments. Also called an air chisel.
air impact wrench
An impact tool powered by compressed air designed to undo tight fasteners.
air nozzle
A compressed air device that emits a fine stream of compressed air for drying or cleaning parts.
air pump
A device used to pump air to the exhaust stream to ensure the converter has enough oxygen to perform gas conversions.
air ratchet
A ratchet tool for use with sockets powered by compressed air.
air spring
A part that provides the springing action or auxiliary spring. It is typically used in air suspension systems or heavy truck applications.
air supply system
Equipment in a motor vehicle that delivers air to the engine.
air switching valve
The valve used to switch secondary air from near the exhaust valve (upstream) to the catalytic converter (downstream) for the purpose of oxidizing hydrocarbons and carbon monoxide.
air drier
A device fitted to compressed air lines to remove moisture.
air-conditioning compressor clutch
The mechanical coupler that is electromagnetically engaged and provides a way of uncoupling the compressor from the accessory drive belt.
air-conditioning machine
A machine designed to recover, recycle, evacuate, leak test, and recharge (R/R/R) the air-conditioning system.
air-conditioning pressure sensor
A sensor that gives an input signal of refrigerant pressure in the air-conditioning system to the ECU.
air-conditioning system pressure
The refrigerant pressure contained within the air-conditioning system.
air-operated braking systems
A braking system that uses compressed air operating on large-diameter diaphragms to provide force to the braking assembly; also called air brakes.
air-operated braking system
A braking system that uses compressed air operating on large-diameter diaphragms to provide force to the braking assembly; also called air brakes.
aldehyde
A pollutant/irritant in diesel fuel.
aldehydes
A pollutant/irritant in diesel fuel.
all-wheel drive (AWD)
A drive train arrangement in which all of the wheels drive the vehicle.
Allen wrench
A type of hexagonal drive mechanism for fasteners.
Allen wrenches
A type of hexagonal drive mechanism for fasteners.
alloy
The mixture of materials to make a substance that has properties different from the original materials. Aluminum alloy has silica added to make it perform better than pure aluminum.
alternating current (AC)
A type of current flow that flows back and forth.
alternating current (AC)
A type of current flow that flows back and forth.
alternative fuel
A nonpetroleum-based motor fuel.
aluminum rod
A lightweight, strong, either cast or forged metal shaft that connects the piston assembly to the crankshaft assembly.
ambient air temperature sensor
A thermistor that is used to measure the air temperature outside the vehicle.
American Petroleum Institute (API)
The organization responsible for setting the standards for all American petroleum products including natural gas and biodiesel fuels.
American wire gauge (AWG)
A standard used to identify different wire sizes.
ammeter
A device used to measure current flow.
amp
An abbreviation for amperes, the unit for current measurement.
anchor pin
A component of the backing plate that takes all of the braking force from the brake shoes.
anemometer
A device that measures airflow in feet per minute (fpm).
angle grinder
A portable grinder for grinding or cutting metal.
anisotropic
An object that has unequal physical properties, along its various axes. Used in head gaskets to pull heat laterally from the edge surrounding the combustion chamber to the water jacket.
anode
A positively charged electrode or plate.
anti-friction bearings
Wheel bearing assemblies that use surfaces that are in rolling contact with each other to greatly reduce friction compared to surfaces in sliding contact.
anti-friction bearing
Wheel bearing assemblies that use surfaces that are in rolling contact with each other to greatly reduce friction compared to surfaces in sliding contact.
anti-lock brake systems (ABS)
A safety measure for the braking system that uses a computer to monitor the speed of each wheel and control the hydraulic pressure to each wheel to prevent wheel lock-up.
anti-lock brake system (ABS)
A safety measure for the braking system that uses a computer to monitor the speed of each wheel and control the hydraulic pressure to each wheel to prevent wheel lock-up.
antibinding
The release of something when it gets stuck.
antifoaming agents
Oil additives that keep oil from foaming as it moves through the engine.
applied force
Pressure placed on something.
arc joint pliers
Pliers with parallel slip jaws that can increase in size. Also called Channel locks.
arm
The primary load-bearing element of a vehicle’s suspension system, commonly known as control arm. Can also mean the steering arm, which applies the driver’s turning effort to the steering knuckle.
armature
The rotating wire coils in motors and generators. It is also the moving part of a solenoid or relay, and the pole piece in a permanent magnet generator.
arms
The primary load-bearing element of a vehicle’s suspension system, commonly known as control arm. Can also mean the steering arm, which applies the driver’s turning effort to the steering knuckle.
asbestos
A mineral with needle-like fibers that can become embedded in lung tissue and cause cancer.
aspect ratio
The ratio of sidewall height to section width of a tire.
aspirator
A tube that is used to direct airflow across the cabin air temperature sensor.
asymmetric tread patterns
A tread pattern that differs on each side and, therefore, is usually directional.
asymmetric tread pattern
A tread pattern that differs on each side and, therefore, is usually directional.
Atkinson cycle
An engine cycle that uses a longer effective power stroke than intake stroke to increase engine efficiency and reduce exhaust emissions. This type of engine is widely used in hybrid-electric vehicles
atmospheric pressure
The pressure of the air surrounding everything caused by gravity and the weight of air. The higher from sea level, the lower the atmospheric pressure.
attenuator
A device that reduces the power of a signal without distorting its waveform.
attenuators
A device that reduces the power of a signal without distorting its waveform.
automatic brake self-adjuster
A system on drum brakes that automatically adjusts the brakes to maintain a specified amount of running clearance between the shoes and drum.
automatic climate control system
A system that automatically adjusts the heating or cooling to meet a specified temperature demanded by the passengers.
automatic fuel limiter
A special refueling port and an overfill protection device fitted on LPG tanks, which ensure that the tank cannot be filled past the safe fill limit of 80%.
automatic load-adjustable shock absorbers
Typically, an air shock absorber used in an automatic load-sensing system that adjusts ride height (ground clearance) automatically such as when additional weight is added to the vehicle.
automatic oilers
A device fitted to compressed air systems to oil air tools.
automatic ride control actuator
An electric stepper motor mounted on top of the shock that changes orifice size inside the shock.
automatic
A system that automatically adjusts the heating or cooling to meet a specified temperature demanded by the passengers.
automatic load-adjustable shock absorber
Typically, an air shock absorber used in an automatic load-sensing system that adjusts ride height (ground clearance) automatically such as when additional weight is added to the vehicle.
automatic oiler
A device fitted to compressed air systems to oil air tools.
Automotive Service Excellence (ASE)
An independent, nonprofit organization dedicated to the improvement of vehicle repair through the testing and certification of automotive professionals.
Automotive Youth Educational Systems (AYES)
An independent, nonprofit organization that is a partnership between automotive manufacturers, their dealerships, and affiliated secondary automotive programs.
available voltage
The maximum amount of voltage that the induction coil secondary is capable of putting out.
aviation snips
A scissor-like tool for cutting sheet metal.
axial loads
The load applied in line with a shaft. It can be controlled with thrust bearings.
axial piston compressor
A design of compressor that uses an angled plate (swash plate) to create the piston movement.
axial load
The load applied in line with a shaft. It can be controlled with thrust bearings.
axle
The shaft of the suspension system to which the tires and wheels are attached; used to transmit driving torque to the wheels.
axles
The shaft of the suspension system to which the tires and wheels are attached; used to transmit driving torque to the wheels.
B
B100 fuel
A fuel that is 100% biodiesel (“neat”).
B20 fuel
A fuel that is 20% biodiesel blended with 80% petrodiesel.
back clearance
The area or space behind the piston rings when the rings are in the piston ring grooves.
backing plate
A stamped steel plate, bolted to the steering or suspension, which supports the wheel cylinder, brake shoes, and other hardware.
backing plate (disc brakes)
A metal plate to which the brake lining is fixed.
backlash clearance
The amount of movement between the pinion teeth versus the ring teeth.
baffle
A plate installed vertically in the fuel tank to control sloshing of the fuel.
baffles
Plates installed vertically in the fuel tank to control sloshing of the fuel.
balance shafts
A metal shaft attached and located inside the engine cylinder block assembly to counteract crankshaft vibrations.
balance shaft
A metal shaft attached and located inside the engine cylinder block assembly to counteract crankshaft vibrations.
ball bearings
The rolling components of a wheel bearing consisting of hardened balls that roll in matching grooves in the inner and outer races.
ball hone
An assembly of metal rods, with abrasive stones attached, that is inserted into the cylinder and spun to break the glazing off the cylinder walls and make a new crosshatched pattern.
ball joints
A swivel connection mounted in the outer end of the front control arm. These swivels are typically constructed with a ball and socket to allow pivoting.
ball joint
A swivel connection mounted in the outer end of the front control arm. These swivels are typically constructed with a ball and socket to allow pivoting.
ball-peen (engineer’s) hammer
A hammer that has a head that is rounded on one end and flat on the other; designed to work with metal items.
ball-return guides
A special passage or metal tube through which the balls move in recirculating ball steering boxes.
ball-return guide
A special passage or metal tube through which the balls move in recirculating ball steering boxes.
ballast resistor
Used to limit the amount of current flowing in the ignition primary circuit.
ballast
A device that increases lighting voltage substantially and controls the current to the bulb.
band brake
A braking system that uses a metal band lined with friction material to clamp around the outside of a wheel or drum.
band
A metal band with friction material bonded to one side. The band is contracted around a drum to stop the drum from spinning.
bar
A metric unit of measure for pressure.
barometric pressure (BARO) sensor
A sensor that measures atmospheric pressure.
barrier cream
A cream that looks and feels like a moisturizing cream but has a specific formula to provide extra protection from chemicals and oils.
barrier-type hose
A rubber hose made with a nylon bladder inside to contain substances with small molecular structures, such as R-134a.
bars
A metric unit of measure for pressure.
base circle
The rounded bottom part of the camshaft (off the lobe) where the valves remain closed or at rest.
batteries
An electrochemical device used to supply voltage to a vehicle’s electrical systems.
battery chargers
A device that charges a battery, reversing the discharge process.
battery electric vehicle (BEV)
A vehicle powered by battery only.
battery terminal configuration
The placement of positive and negative battery terminals.
battery
An electrochemical device used to supply voltage to a vehicle’s electrical systems.
battery charger
A device that charges a battery, reversing the discharge process.
baulk-ring synchromesh unit
A synchronizer used in all current transmissions. It uses a blocking ring. Also called a blocker ring synchromesh unit.
bead seat
The part of the wheel that the tire seals against.
beam axle
A suspension system in which one set of wheels is connected laterally by a single beam or shaft.
beam-type axle
A rear-wheel drive axle assembly that has a solid tube incorporating the differential gears.
beam-type
A rear-wheel drive axle assembly that has a solid tube incorporating the differential gears.
bearing cage
The component in a wheel bearing that maintains the proper spacing between the roller bearings or ball bearings.
bearing packer
A tool that forces grease into the spaces between the bearing rollers.
bearing races
Hardened metal surfaces that roller or ball bearings fit into when a bearing is properly assembled.
bearing crush
The force created to seat the bearing by the extra bearing material when the ends of the bearing inserts touch each other and are forced against each other.
bearing inserts
Components made out of soft metal materials that are replaceable and come in pairs; also called half-shell bearings.
bedding-in
The process of a valve wearing into the valve seat and creating a positive seal around the whole diameter.
before top dead center (BTDC)
The position of the piston when it has not yet reached top dead center.
belt alternator starter (BAS)
A type of hybrid drive system that uses a belt-driven alternator/starter that operates on 42 volts.
belt routing label
A label that lists a diagram of the serpentine belt routing for the engine accessories.
bench grinder (pedestal grinder)
A grinder that is fixed to a bench or pedestal.
bench vice
A device that securely holds material in jaws while it is being worked on.
bendable tangs
Small tabs on the brake pad backing plate that are crimped on to the caliper, creating a secure fit and reducing noise.
bi-fuel
Two fuels used in a vehicle one at a time, such as compressed natural gas or gasoline.
bias-ply
A tire constructed in a latticed, crisscrossing structure, with alternate plies crossing over each other and laid with the cord angles in opposite directions.
biasply
A tire constructed in a latticed, crisscrossing structure, with alternate plies crossing over each other and laid with the cord angles in opposite directions.
bidirectional control
The ability to command different solenoids and actuators “on” and “off” to check their operation.
bidirectional scanners
Scanners used to monitor engine compression, vacuum, internal engine anomalies, and so forth by causing various components and systems to operate for test purposes.
billet
The roughly shaped steel piece that has been cast or forged but has not undergone its final machining.
bimetal
Aluminum, tin, and silicon alloy metals placed together with steel to form one piece of material and used for bearing materials.
bio-ethanol
A renewable fuel derived from a variety of cellulose-based plants.
biodiesel
Renewable fuel made from organic feedstocks.
biomass
Organic matter used for fuel.
bleeder screw
A screw that allows air and brake fluid to be bled out of a hydraulic brake system when it is loosened and seals the brake fluid in when it is tightened.
bleeding
The process of removing air from a hydraulic braking system.
blind rivet
A rivet that can be installed from its insertion side.
blink codes
Codes used to communicate DTCs; they are given by the EBCM as a series of blinks illuminated by the ABS warning lamp.
block deck
The “top” of the engine block and cylinder bore where the cylinder head is bolted on.
block valve
A style of TXV that has an outlet side like the external valve; however, both the inlet and the outlet pipe go through the block, so the sensing bulb is built into the block.
blocking ring
A synchronizer part that increases or decreases a gear’s speed to match shaft speed so that the synchronizer sleeve can lock the gear to the shaft. Also called baulk ring.
blow-by
Pressure that leaks past the compression rings during compression and combustion.
blow-off valve
A valve that allows the release of excessive boost pressure from the turbocharger when the throttle plate is quickly closed.
blowby gas
The result of combustion gases leaking past the compression rings and getting into the crankcase.
blower motor
An electric motor, usually the permanent magnet type, that moves air over the air conditioning evaporator and heater core.
bob weights
Weights used during the balancing process that are used to mimic the exact weight of the piston and connecting rod weights for that particular rod bearing journal.
body control module (BCM)
The computer that controls the electrical system in the body of a vehicle, including power windows, door locks, heating and A/C systems, and in some cases the EBC system.
body electronic module (BEM)
An electronic control module for body electrical systems.
boiling point
The temperature at which a substance begins to change from a liquid to a gas.
bolt cutters
Strong cutters available in different sizes, designed to cut through non-hardened bolts and other small-stock material.
bolt
A type of threaded fastener with a thread on one end and a hexagonal head on the other.
bolts
A type of threaded fastener with a thread on one end and a hexagonal head on the other.
bonded linings
Brake linings that are essentially glued to the brake pad backing plate; more common on light-duty vehicles.
boost valves
A valve located in the HCU that is controlled by the EBCM; it allows brake fluid under high pressure to flow into the HCU hydraulic circuits to apply the brakes when commanded.
boost valve
A valve located in the HCU that is controlled by the EBCM; it allows brake fluid under high pressure to flow into the HCU hydraulic circuits to apply the brakes when commanded.
bore
The inside surface of a cylinder, or its diameter.
bored out
An object that has been bored.
boring bar
A long bar used to position and align a single-point tool, such as an engine cylinder block boring machine, for boring operations.
bottom dead center (BDC)
The position of the piston at the end of its stroke when it is closest to the crankshaft.
bottoming tap
A thread-cutting tap designed to cut threads to the bottom of a blind hole.
box-end wrench
A wrench or spanner with a closed or ring end to grip bolts and nuts.
brake lathe
A tool used to refinish the drum surface by removing a small amount of metal and returning it to a concentric, non-directional finish.
brake shoes
A steel shoe and brake lining friction material that apply force to the brake drum during braking.
brake shoe adjustment gauge
An adjustable tool used to pre-adjust the brake shoes to the diameter of the brake drum.
brake spoon
A tool used to adjust the brake lining-to-drum clearance when the drum is installed on the vehicle.
brake spring pliers
A tool used for removing and installing brake return springs.
brake switch
The electrical switch that is activated by the brake pedal; it turns on the brake lights and signals the EBCM that the brakes are being applied.
brake assist (BA)
An enhanced safety system built in to some ABS systems that anticipates a panic stop and applies maximum braking force to slow the vehicle as quickly as possible.
brake fade
The reduction in stopping power caused by a change in the brake system such as overheating, water, or overheated brake fluid.
brake pedal emulator
A brake pedal assembly used in electronically controlled braking systems to send the driver’s braking intention to the computer; it mimics the feel of a standard brake pedal.
brake fluid
Hydraulic fluid that transfers forces under pressure through the hydraulic lines to the wheel braking units.
brake hoses
A flexible section of the brake lines between the body and suspension to allow for steering and suspension movement.
brake lines
Made of seamless, double-walled steel, and able to transmit over 1000 psi (6895 kPa) of hydraulic pressure through the hydraulic brake system.
brake booster
A vacuum or hydraulically operated device that increases the driver’s braking effort.
brake lining thickness gauges
A tool used to measure the thickness of the brake lining.
brake pad shims and guides
Small pieces of metal that cushion the brake pad and absorb some of the vibration, helping to cut down on unwanted noise.
brake wash station
A piece of equipment designed to safely clean brake dust from drum and disc brake components.
brake drum
A short, wide, hollow cylinder that is capped on one end and bolted to a vehicle’s wheel; it has an inner friction surface that the brake shoe is forced against.
brake technician
A technician who specializes in working on vehicle brake systems.
brake hose
A flexible section of the brake lines between the body and suspension to allow for steering and suspension movement.
brake lining thickness gauge
A tool used to measure the thickness of the brake lining.
brake shoe
A steel shoe and brake lining friction material that apply force to the brake drum during braking.
brake-by-wire system
A braking system that uses no mechanical connection between the brake pedal and each brake unit. The system uses electrically actuated motors to apply brake force.
brakes
A system made up of hydraulic and mechanical components designed to slow or stop a vehicle.
braking torque
The torque acting to twist the axle housing around its center during braking.
breakdown
The loss of electrical insulation properties.
breaker plate
The movable plate which the breaker points are mounted on and which pivots as the vacuum advance pulls on it.
breather tube
A tube used in the PCV system to allow fresh air into the engine crankcase.
brinelling
Damage done to the surface of a bearing caused by excessive load, which exceeds the limit of the bearing material, typically from shock loads.
British thermal units (Btu)
A measure of heat energy. It takes 1 Btu to raise the temperature of 1 pound of water 1°F.
British thermal unit (Btu)
A measure of heat energy. It takes 1 Btu to raise the temperature of 1 pound of water 1°F.
broach-style surfacer
A tool used in resurfacing the engine block.
brushless
An electric motor without brushes.
brushless DC motor
An electric motor that does not have any brushes and is sometimes called an “electronically commutated motor.” In this type of motor, an electronic control module replaces the brushes and commutator.
bucket-style lifters
A bucket-shaped lifter assembly that sits on top of the valves and is operated directly by the camshaft. It can be hydraulic or mechanical.
bucket-style lifter
A bucket-shaped lifter assembly that sits on top of the valves and is operated directly by the camshaft. It can be hydraulic or mechanical.
bump steer
The undesired condition produced when hitting a bump where the vehicle darts to one side as the steering linkage is pushed or pulled as a result of the travel of the suspension.
burn rate
The rate of flame spread for liquid or gaseous fuel.
bus
A system of networking circuits in which various on-board modules are connected to one another, allowing the exchange of information between them.
bushing
An insert with an inner bearing surface that is fitted into a hole in an object, allowing the object to rotate or slide on a pin or shaft.
bushings
An insert with an inner bearing surface that is fitted into a hole in an object, allowing the object to rotate or slide on a pin or shaft.
butt connectors
A crimp or solder joint that creates a permanent connection.
butt connector
A bucket-shaped lifter assembly that sits on top of the valves and is operated directly by the camshaft. It can be hydraulic or mechanical.
bypass filter
An oil filter system that only filters some of the oil.
bypass valve
The pressure control valve of the supercharger. When the bypass valve opens, it lets air move around the supercharger compressor section, reducing the boost pressure.
C
C-clamp
A clamp shaped like the letter C; it comes in various sizes and can clamp various items.
cabin air temperature sensor
A thermistor that measures air temperature inside the vehicle.
caliper
A hydraulic device that uses pressure from the master cylinder to apply the brake pads against the rotor.
caliper dust boot seal driver set
A set of drivers used to install metal-backed caliper dust boot seals.
caliper piston pliers
A tool used to grip caliper pistons while removing them.
caliper piston retracting tool
A tool used to retract caliper pistons on integrated parking brake systems.
cam
The egg-shaped lobe machined to a shaft used to cause opening and closing of the valves of a four-stroke cycle engine.
cam angle sensor
A sensor that measures cam angle position.
cam lobe centerline
The location of the cam lobe in relation to top dead center of the engine in degrees.
cam lobe ramp
The rise of the lobe from the base circle to the top of the lobe, which is where the valve starts to lift, on the side opposite of where it starts to close.
cam lobe separation
The number of degrees between the centerline of the intake lobe and the centerline of the exhaust lobe; this with cam duration determines the amount of valve overlap.
cam lobes
Raised areas or protrusions on an otherwise round shaft.
cam-in-block engines
An engine in which the camshaft is located in the engine block rather than on the cylinder head.
cam-in-block engine
An engine in which the camshaft is located in the engine block rather than on the cylinder head.
camber
The side-to-side vertical tilt of the wheel. It is viewed from the front of the vehicle and measured in degrees. Negative camber is when the top of the tire is closer to the center of the vehicle than the bottom of the tire.
camshaft
A shaft with lobes that operates the valve mechanisms controlling valve opening time and duration. Also, it can be used to drive fuel injection pumps and mechanical fuel pumps.
camshaft follower
A slider or roller placed in direct contact with the lobes of the OHC camshaft that pushes on the tip of the valve to open it.
camshaft lobe
The eccentric “egg-shaped” portion of the camshaft that pushes on the valve lifter or camshaft follower.
camshaft position (CMP) sensor
A sensor mounted near the camshaft and used to send camshaft and valve position information to the PCM.
camshaft position sensor
A sensor mounted near the camshaft and used to send camshaft and valve position information to the PCM.
camshaft followers
A slider or roller placed in direct contact with the lobes of the OHC camshaft that pushes on the tip of the valve to open it.
CAN-bus circuit
A two-wire communication network that transmits status and command signals between control modules in a vehicle.
canted valves
A valve arrangement in the cylinder head where the valves are at an angle to the cylinder bore. Canting the valves can make for a straighter path for air to flow into and out of the intake and exhaust ports.
capacitance
The ability of a capacitor to store an electrical charge.
capacitor
A device that can quickly store a small amount of electrical energy, at which point it is charged.
carbon dioxide (CO ₂ )
A vehicle emission that is considered a primary greenhouse gas, though not toxic and not yet regulated.
carbon monoxide (CO)
A vehicle emission produced by partially burned fuel that is colorless, odorless, and highly toxic and that causes asphyxiation when inhaled.
carbon monoxide poisoning
Exposure to higher than tolerable levels of carbon monoxide, resulting in headaches, fatigue, or loss of consciousness, eventually resulting in death.
Carbon dioxide
A vehicle emission that is considered a primary greenhouse gas, though not toxic and not yet regulated.
carbon monoxide
A vehicle emission produced by partially burned fuel that is colorless, odorless, and highly toxic and that causes asphyxiation when inhaled.
carburetor float bowl
The part of the carburetor that holds fuel to be burned in the engine; the bowl is at a constant level of fuel to ensure adequate fuel is present during driving.
carrier
The part of the throw-out bearing assembly that holds the bearing.
casing plies
A network of cords that give the tire shape and strength; also known as casing cords.
cast rod
A connecting rod that is created by the metal casting process.
castellated nut
An adjusting nut with slots cut into the top such that it resembles a castle; used with a cotter pin to prevent the nut from turning.
caster
The angle formed through the wheel pivot points when viewed from the side in comparison to a vertical line through the wheel.
casting line
A by-product of the metal casting process that forms a line found on parts that are cast in metal.
catalyst
A device that changes chemical composition without self-destruction.
cathode
A negatively charged electrode or plate.
center bolt
A fastener or bolt found in the middle of the harmonic balancer or cam sprocket that attaches it to the crankshaft or the camshaft.
center electrode
The electrode located in the center of a spark plug. It is the hottest part of the spark plug.
center punch
Less sharp than a prick punch, the center punch makes a bigger indentation that centers a drill bit at the point where a hole is required to be drilled.
centerline
The imaginary line drawn down the exact center of the vehicle from front to back.
centrifugal advance mechanism
An ignition timing device, located above or beneath the distributor base plate, that rotates with the distributor cam and is used to advance the spark. As engine speed rises, the flyweights on the advance mechanism are thrown outward by centrifugal force. Since the distributor cam is able to pivot on the distributor shaft, the weights act against their springs and move the distributor cam forward.
centrifugal force
A force pulling outward on a rotating body.
centrifugal switch
A switch that is only activated when centrifugal forces are placed on a vehicle.
cetane number
A rating of the ignition quality of diesel fuel.
chamfer
A rounded or angled edge located on the blocking ring, with ridges machined into it to help grab the cone surface of the gear.
chamfering
The process of cutting into the top of the oil passage hole with a specialized chamfering tool or regular drill bit to make the top of the oil hole more like a 45-degree angle, to keep the edge from digging into the bearing the way a 90-degree edge would.
channel
The number of wheel speed sensor circuits and hydraulic circuits the EBCM monitors and controls.
charcoal canister
A device used to trap the fuel vapors. The fuel vapors adhere to the charcoal, until the engine is started, and engine vacuum can be used to draw (purge) the vapors into the engine so that they can be burned along with the air–fuel mixture.
charge (electrical)
In measuring capacitance, the amount of electrical energy present.
charge (heating and cooling system)
The amount of refrigerant present in the system or the process of installing refrigerant in the system.
charge carriers
A mobile particle that has a positive or negative electrical charge.
charge
The amount of refrigerant present in the system or the process of installing refrigerant in the system.
charge carrier
A mobile particle that has a positive or negative electrical charge.
P
PT chart
A pressure-temperature chart that shows the relationship between air-conditioning pressures and evaporator temperature.
C
chassis dynamometer
A machine with rollers that allows a vehicle to attain road speed and load while sitting still in the shop.
chassis technician
A technician who specializes in working on vehicle suspension and steering systems.
chassis
The main support frame in a vehicle to which the drive train and body components are connected.
check valve
Also known as a shuttle valve, a valve that allows the flow of hydraulic oil in one direction only. It is typically used to allow oil to escape quickly from an application device when shifting gears.
check valves
Also known as a shuttle valve, a valve that allows the flow of hydraulic oil in one direction only. It is typically used to allow oil to escape quickly from an application device when shifting gears.
chlorofluorocarbon (CFC)
A manufactured compound designed to be used as a refrigerant. It is now illegal due to the high chlorine content.
chlorofluorocarbons (CFCs)
A manufactured compound designed to be used as a refrigerant. It is now illegal due to the high chlorine content.
choke
A device that provides a rich air–fuel mixture until the engine warms up by restricting the flow of air at the entrance to the carburetor, before the venturi.
circuit breakers
A device that trips and opens a circuit, preventing excessive current flow in a circuit. It is resettable to allow for reuse.
circuit or schematic diagrams
A pictorial representation or road map of the wiring and electrical components.
circuit breaker
A device that trips and opens a circuit, preventing excessive current flow in a circuit. It is resettable to allow for reuse.
circuit or schematic diagram
A pictorial representation or road map of the wiring and electrical components.
Clean Air Act (CAA)
Federal legislation enacted in the United States to reduce pollution, in part from automobiles.
Clean Air Act
A policy signed into law in 1990 that sets standards for air pollution to eliminate ozone-depleting elements.
cleaning gun
A device with a nozzle controlled by a trigger fitted to the outlet of pressure cleaners.
climate control systems
A system that provides the heating and cooling of air inside the passenger compartment for passenger comfort.
climate control system
A system that provides the heating and cooling of air inside the passenger compartment for passenger comfort.
clock spring
A special rotary electrical connector located between the steering wheel and the steering column that maintains a constant electrical connection with the wiring system while the vehicle’s steering wheel is being turned.
closed loop
The operational status of the engine control system in which the oxygen sensor is providing feedback of rich or lean exhaust conditions and the control unit is varying fuel delivery based on that information.
closed loop system
A totally self-contained system with no materials entering or exiting.
cloud point
The temperature at which wax (paraffin) in diesel fuel starts to solidify.
clutch binding
A condition in which the clutch disc is dragging, leading to grinding gears during gear shifts and possibly clutch chatter.
clutch chatter
A condition in which the clutch shudders when the clutch pedal is released, and the vehicle starts to move forward.
clutch disc
The center component of the clutch assembly, with friction material riveted on each side. Also called a clutch plate or friction disc.
clutch electrical winding
An electromagnetic control device that creates a magnetic field that pulls in the clutch to make contact with the pulley.
clutch fork
The part of the clutch linkage that operates the throw-out bearing.
clutch pedal
The foot-operated pedal used by the driver to engage and disengage the clutch.
clutch safety switch
An electrical switch that is operated by the clutch pedal and keeps the starter motor from cranking the engine over until the clutch is fully depressed.
clutch system
A mechanically operated assembly that connects and disconnects the engine from the transmission.
coarse (UNC)
Used to describe thread pitch; stands for Unified National Coarse.
code
A code set by the computer indicating system or component malfunction.
codes
A code set by the computer indicating system or component malfunction.
coefficient of friction
A value assigned to materials to describe the amount of friction when two objects slide against each other.
coil bind
A result of excessive valve lift. When the coils of the spring touch each other, the spring breaks, flattening the cam lobe and bending the pushrod.
coil spring pressure plate
A type of pressure plate that uses coil springs to provide the clamping force.
coil springs
Spring steel wire that is heated and wound into a coil that is used to support the weight of a vehicle.
coil spring
Spring steel wire that is heated and wound into a coil that is used to support the weight of a vehicle.
coil-on-plug
A type of ignition system used on late-model vehicles that uses one coil placed above each spark plug.
cold chisel
The most common type of chisel, used to cut cold metals. The cutting end is tempered and hardened so that it is harder than the metals that need to be cut.
cold cranking amps (CCA)
A standard for rating the ability of a vehicle battery to supply high current under cold operating conditions.
collet
A cone-shaped tool that encloses and grips a rod or shaft when inserted into the sleeve of a lathe or other machine.
column inertia
The principle that as a column of air flows, it creates inertia, which keeps air flowing until its inertia energy is spent; sometimes referred to as a “ram effect” when using tuned intake or exhaust systems.
combination pliers
A type of pliers for cutting, gripping, and bending.
combination wrench
A type of wrench that has an open end on one end and a box-end wrench on the other.
combustion chamber
The area of an engine in which the air/fuel mixture is burnt. It consists of the bottom of the cylinder head and the top of the piston.
combustion pressure
The force exerted by the expanding gases during the burning process. It is what causes the internal combustion engine to operate.
common bore
When a single cylinder is used for two pistons. A tandem master cylinder would be an example of two pistons in one bore.
common rail system (CRS)
A diesel fuel injection system that uses a pump to develop high-pressure fuel directed to an accumulator or rail.
common rail
A type of injection system using a common fuel manifold from which individual injectors are fed high-pressure fuel.
commutator
A device made on armatures of electric generators and motors to control the direction of current flow in the armature windings.
companion flange
A splined flange that transmits power from the drive shaft to the pinion gear.
compensating port
Connects the brake fluid reservoir to the master cylinder bore when the piston is fully retracted, allowing for expansion and contraction of the brake fluid.
compliance bushing
A rubber bushing with a voided section molded in it that allows component movement under torque application. It is typically used in control arms on front-wheel drive vehicles to minimize torque steer issues.
complicated fracture
A fracture in which the bone has penetrated a vital organ.
compound planetary gear sets
Two or more simple planetary gear sets connected together.
compound planetary gear set
Two or more simple planetary gear sets connected together.
compressed air equipment
Tool or machinery that operates on compressed air.
compressed natural gas (CNG)
Methane compressed for on-board storage in cylinders.
compressed natural gas vehicles (CNGVs)
A vehicle that uses methane stored in high-pressure cylinders.
compressed natural gas vehicle (CNGV)
A vehicle that uses methane stored in high-pressure cylinders.
compression ratio (CR)
The volume of the cylinder with the piston at bottom dead center as compared to the volume of the cylinder at top dead center, given in a ratio such as 9:1 CR.
compression ring grooves
A square groove found on the outside of the piston skirt in which the piston ring fits.
compression stroke
The stroke in an engine cycle when the piston moves up with the valves closed, compressing the air trapped in the cylinder.
compression tester
A device used to measure the amount of compression pressure a cylinder can generate.
compression ring
A metal ring found inside the grooves on the side of the engine piston.
compression ratio
The volume of the cylinder with the piston at bottom dead center as compared to the volume of the cylinder at top dead center, given in a ratio such as 9:1 CR.
compression ring groove
A square groove found on the outside of the piston skirt in which the piston ring fits.
compression rings
A metal ring found inside the grooves on the side of the engine piston.
compression-ignition engine
An engine that uses the heat of compression to ignite the air–fuel mixture; also known as a diesel engine.
compression-ignition (CI) engine
An engine that uses the heat of compression to ignite the air–fuel mixture; also known as a diesel engine.
compression-ignition (CI) engines
An engine that uses the heat of compression to ignite the air–fuel mixture; also known as a diesel engine.
compressor
A belt or electrically driven device designed to increase refrigerant pressure and cause refrigerant to travel through the air-conditioning system.
compressor surge
The backup of air against the throttle plate as it is closed. The turbocharger is still spinning, pressurizing air, when the throttle plate is closed. Air will stack up, creating a rapid slowing of the turbocharger compressor wheel. This can damage the compressor wheel.
computer-controlled carburetor
A carburetor that changes and sets air–fuel ratio based on commands from a PCM that uses memory and input from sensors.
concentric interrupter rings
Two interrupter rings that have the same center.
concentricity (valve)
A term used to describe a valve seat where the valve seat and valve stem share a common center. In this design, the valve can seal against the seat no matter how it is rotated.
concentricity
The roundness of a hole. If the hole is not round it can also be referred to as out of round.
concentricity (hole)
The roundness of a hole. If the hole is not round it can also be referred to as out of round.
condensation
The changing of a gas into a liquid through cooling.
condenser
The air conditioning component located in the front of the vehicle designed to allow high-pressure refrigerant to change states from gas to liquid.
condenser (capacitor)
A self-contained unit that is connected electrically in parallel with the contact breaker points and used to assist the rapid collapse of the magnetic field in the coil by preventing the contact breaker points from arcing. Also used on some coils to reduce radio frequency interference.
conduction
The process of transferring heat through matter by the movement of heat energy through solids from one particle to another.
conductor
A material that allows electricity to flow through it easily. It is made up of atoms with one to three valance ring electrons.
conductors
A material that allows electricity to flow through it easily. It is made up of atoms with one to three valance ring electrons.
connecting rod
A cast or forged metal rod that connects the engine pistons to the engine crankshaft.
connector
The plastic housing on the end of a wiring harness that holds the wire terminals in place. It can also refer to a type of wire terminal that connects wires together or to a common point such as a bolt.
connectors
The plastic housing on the end of a wiring harness that holds the wire terminals in place. It can also refer to a type of wire terminal that connects wires together or to a common point such as a bolt.
conservation of energy
A physical law that states that energy cannot be created or destroyed.
constant mesh
A term used to describe two or more parts, such as gears, that are in constant contact with each other.
constant velocity (CV) joints
Joints commonly used in front-wheel drive vehicles to allow flexibility of the axle while turning.
constant-velocity (CV) joint
Joints commonly used in front-wheel drive vehicles to allow flexibility of the axle while turning.
contact breaker point ignition system
A type of ignition system that uses a mechanical means of turning the primary circuit on and off.
contact breaker points
A mechanically operated electrical switch that is fixed to the distributor base plate and opened and closed by the distributor cam with the rotation of the engine. The contacts normally form a self-contained unit, fixed to the base plate by a retaining screw engaged in a slot in the fixed contact.
continuity
A conductive path between two points.
continuous monitoring
A term that describes OBDII monitors that run continuously throughout the drive cycle.
continuously variable transmission (CVT)
A type of transmission that has no fixed gears, as in a conventional transmission, but rather can adjust gear ratios infinitely within the design of the transmission.
continuously variable transmissions (CVTs)
A type of transmission that has no fixed gears, as in a conventional transmission, but rather can adjust gear ratios infinitely within the design of the transmission.
continuously variable transmissions (CVT)
A type of transmission that has no fixed gears, as in a conventional transmission, but rather can adjust gear ratios infinitely within the design of the transmission.
control arm
The primary load-bearing element of a vehicle’s suspension system, commonly referred to as an A-arm or wishbone. These arms may be used as an upper and lower pivot point for the wheel assembly. They attach to the chassis with rubber bushings that allow up-and-down movement of the tire and wheel assembly.
control module
A generic term that identifies an electronic unit that controls one or more electrical systems in the vehicle; also called a control unit.
control unit
Any device that controls another object such as a computer.
controlled area network bus (CAN-bus)
A wire data network found in vehicles to connect control modules, so they can communicate quickly and easily.
controller area networks (CANs)
A localized (onboard) vehicle network that enables computers and components to send and receive signals across a shielded twisted pair of wires.
controller area network (CAN)
A localized (onboard) vehicle network that enables computers and components to send and receive signals across a shielded twisted pair of wires.
convection
The process of transferring heat by the circulatory movement that occurs in a gas or fluid as areas of differing temperatures exchange places due to variations in density and the action of gravity.
conventional oil
Oil that is processed from crude oil; about 20% of oil is additives.
conventional theory
The theory that electrons flow from positive to negative.
convertible
A vehicle that converts from having an enclosed top to having an open top by a roof that can be removed, retracted, or folded away.
coolant
When anti-freeze concentrate is mixed with water, the resulting mixture is called engine coolant. Most manufacturers recommend a 50/50 mixture.
coolant control valve
A valve that blocks off coolant flow to keep hot water from entering the heater core when less heat is requested by the operator.
coolant temperature sensor (CTS)
A thermistor usually screwed into a cylinder head water jacket. Usually the CTS is a negative temperature coefficient thermistor, or a resistor whose resistance varies, with temperature varying a voltage signal to the PCM.
coolant label
A label that lists the type of coolant installed in the cooling system.
cooler flow test
The placement of a specialty measuring device into the transmission cooler line to measure fluid flow to the cooler. Low cooler flow can be a sign of other issues with the pump and lubrication system.
cooling hoses
Flexible hoses that connect the stationary components of the cooling system, such as heater core and radiator, to the engine, which is mounted on flexible mounts.
core plugs
A metal cap for the holes that are used to remove core sand used during the casting process.
core plug
A metal cap for the holes that are used to remove core sand used during the casting process.
cored solder
Solder that is in the form of a hollow wire. The center is filled with flux, which is used as a cleaning agent while the solder is being applied to the metal surfaces.
cornering force (suspension system)
The force applied to an axle that shifts the axle in relation to the position of the body when turning.
cornering force (wheels)
The force between the tread and the road surface as a vehicle turns.
cornering force
The force applied to an axle that shifts the axle in relation to the position of the body when turning.
corona-suppression
An electronic sniffer used for detecting refrigerant leaks.
corrosion inhibitors
Oil additives that keep acid from forming in the oil.
cotter pin
A one-use soft metal pin that can be bent into shape and is used to retain bearing adjusting nuts.
counter-electromotive force (CEMF)
Voltage created in the field windings as the motor rotates, which opposes battery voltage and limits motor speed.
coupe
A two-door vehicle that has seating for two people and may have a small rear seat.
crank angle position
The position of the crankshaft, measured in degrees.
crank angle sensor
A sensor that measures crank angle position.
crank core
The rough, unfinished crankshaft assembly that has just left the foundry or forging area.
crank angle sensors
A sensor that measures crank angle position.
crankcase
The bottom area of the engine cylinder block where the crankshaft is located.
cranking amps (CA)
A standard similar to CCA, but that measures the battery’s function at a higher temperature—32°F (0°C).
cranking
Rotating the engine by turning the ignition key to the start position.
crankshaft
A part mounted in the lower side of the engine block that has offset journals that rotate to change the up-and-down motion of the pistons into rotary motion at the crankshaft.
crankshaft end play
The amount of forward and rearward movement of the crankshaft in the main bearings. Crankshaft end play is controlled by the engine main bearing thrust bearing.
crankshaft journal
Smooth, curved, machined areas where other parts fit to the crankshaft.
crankshaft position (CKP) sensor
A sensor used by the PCM to monitor engine speed. It can be one of three types of sensors—Hall effect, magnetic pickup, or optical.
crankshaft position sensor
A sensor used by the PCM to monitor engine speed. It can be one of three types of sensors—Hall effect, magnetic pickup, or optical.
crankshaft journals
Smooth, curved, machined areas where other parts fit to the crankshaft.
crescent pump
An oil pump that uses a crescent shaped part to separate the oil pump gears from each other, allowing oil to be moved from one side of the pump to the other.
crimp
The bent shape of the oil ring expander that allows it to provide outward force on the oil rings.
crimps
The bent shape of the oil ring expander that allows it to provide outward force on the oil rings.
cross-arm
A description for an arm that is set at right angles or 90 degrees to another component.
cross-cut chisel
A type of chisel for metal work that cleans out or cuts key ways.
cross-flow radiator
A radiator that uses cooling tubes that run horizontal with tanks on each end. This design allows lower hood profile for better vehicle aerodynamics.
crosshatch
A pattern of lines placed at angles to each other, appearing as a series of Xs across a surface.
crude oil
Material pulled from the earth, originating from organic compounds broken down over time and formed into petroleum. This material is processed in a refinery to break down into various hydrocarbon substances such as diesel, gasoline, and mineral oil, among others.
crush sleeve
A collapsible spacer between the bearings that provides a means of maintaining a preset torque on the pinion nut.
cubic boron nitride (CBN) cutter
An engine block resurfacing tool used on cast iron parts.
current clamp
A device that clamps around a conductor to measure current flow. It is often used in conjunction with a DVOM.
current flow
The flow of electrons, typically within a circuit or component.
curved files
A type of file that has a curved surface for filing holes.
curved file
A type of file that has a curved surface for filing holes.
cylinder bore
The hole in the engine block that the piston fits into.
cylinder head
The part of the engine that is bolted to the engine block and caps off the top of the combustion chamber.
cylinder leakage tester
A device that pumps air into the cylinder and measures the percentage of air that is leaking out of the cylinder.
cylindrical roller bearing assemblies
A type of wheel bearing with races and rollers that are cylindrical in shape and roll between inner and outer races, which are parallel to each other.
cylindrical roller bearing assembly
A type of wheel bearing with races and rollers that are cylindrical in shape and roll between inner and outer races, which are parallel to each other.
D
data link connector (DLC)
The connector through which the scan tool communicates to the vehicle’s computers; it will display the readings from the various sensors and can retrieve trouble codes, freeze frame data, and system monitor data.
dead axles
An axle that does not have the capability to drive the vehicle. It is usually found on the rear of front-wheel drive vehicles.
dead blow hammer
A type of hammer that has a cushioned head to reduce the amount of head bounce.
dead axle
An axle that does not have the capability to drive the vehicle. It is usually found on the rear of front-wheel drive vehicles.
deceleration
A decrease in a vehicle’s speed.
deck
The surface area at the top of the engine block against which the cylinder head seals.
deep dish wheels
A wheel with negative offset, which gives the outside of the wheel a deep dish appearance. Deep dish refers to the side of the wheel that is farthest from the drop center.
deep dish wheel
A wheel with negative offset, which gives the outside of the wheel a deep dish appearance. Deep dish refers to the side of the wheel that is farthest from the drop center.
deflecting force
A force that moves an object in a different direction or into a different shape.
degree wheel
A disc with 360 one-degree markings near its outer edge; it bolts to the front of the crankshaft and is used to check valve and cam timing.
degrees of distributor rotation
A measure of the amount that the distributor rotates, where one complete circle is equal to 360 degrees.
delay circuits
A combination of electrical and electronic components that provide a time delay for switching an electrical circuit.
delay circuit
A combination of electrical and electronic components that provide a time delay for switching an electrical circuit.
U
US Department of Transportation (DOT)
A federal agency that regulates transportation safety in the United States, including vehicles’ wheels and tires. The DOT requires a code—a series of letters and numbers—to be stamped into the sidewall of every tire made for public use in the United States. These codes contain information such as the date of manufacture and the plant where the tire was manufactured.
D
depletion layer
An area of neutral charge in semiconductors.
depth filter
A hydraulic filter that has thick filter media to trap dirt and other particles of various sizes as they pass through the filter.
depth micrometers
A measuring device that accurately measures the depth of a hole.
depth micrometer
A measuring device that accurately measures the depth of a hole.
desiccant
A drying agent used in air-conditioning systems to absorb moisture.
detent mechanism
The mechanism that holds or helps hold the shift rail into position to ensure that the gear does not pop out when selected and to let the driver feel when a shift is completed.
detent valve
A type of spool valve that is connected to the throttle on the vehicle. The valve is used to force a downshift when the throttle is opened all the way, assuming the governor pressure is below a specified point. Kickdown valves are also called detent valves.
detergents
Oil additives that help to keep carbon from sticking to engine components.
detonation
The condition in which the remaining fuel charge fires or burns too rapidly after the initial combustion of the air–fuel mixture. It is audible through the combustion chamber walls as a knocking noise.
diagnostic trouble codes (DTCs)
A code set by the computer indicating system or component malfunction.
diagnostic trouble code (DTC)
A code set by the computer indicating system or component malfunction.
diagonal cutting pliers
Cutting pliers for small wire or cable.
dial indicators
An accurate measuring device where measurements are read from a dial and needle.
dial bore gauge
An accurate measuring device for inside bores, usually made with a dial indicator attached to it.
dial indicator
An accurate measuring device where measurements are read from a dial and needle.
diaphragm pressure plate
A slightly conical, spring steel plate used to provide the clamping force for the clutch assembly.
diaphragm-style EGR valve
An EGR valve that is operated by a diaphragm that moves when vacuum is applied to it, opening a passageway for exhaust to flow.
dichlorodifluoromethane (R-12)
An inert, colorless gas that can be used as a refrigerant. It is stored in white containers.
die stock
A handle for securely holding dies to cut threads.
diesel exhaust fluid (DEF)
A mixture of urea and water that is injected into the exhaust system of a late-model diesel-powered vehicle to reduce exhaust nitrogen oxide emissions.
diesel particulate filter (DPF)
A filter that converts particulate matter, or soot, into ash.
dieseling
A condition in which the engine continues to run after the ignition key is turned off. Also referred to as run-on.
differential gear set
The arrangement of gears between two axles that allows each axle to spin at its own speed when the vehicle is going around a corner.
differential gears
Gears situated in the final drive assembly that are meshed together and with both axles, allowing the wheels to rotate at different speeds when turning a corner.
digital volt-ohmmeter (DVOM)
A test instrument with a digital display for measuring voltage, resistance, and current. Also called a digital multimeter (DMM).
diode
A two-lead electronic component that allows current flow in one direction only.
dipper
A type of splash lubricating system used in small engines. It works like a spoon scooping up oil and throwing it upward onto the crankshaft and other wear surfaces.
direct burning
The phase of combustion after ignition when the rest of the fuel is injected into the combustion chamber and there is a more gradual pressure change in the cylinder.
direct current (DC)
Movement of current that flows in one direction only.
direct drive
A condition in which the engine and transmission output are turning at the same rate of speed.
direct fuel injection
A fuel injection system in which the fuel is injected directly into the combustion chamber.
direct ignition system
May refer to a waste spark ignition or a coil-on-plug ignition system, in which the coils are directly attached to the spark plugs.
direct TPMS
A type of automated tire pressure monitoring system that measures tire pressure and possibly temperature via a sensor installed inside each wheel.
direct
A fuel injection system in which the fuel is injected directly into the combustion chamber.
direct-acting telescopic shock absorber
A shock absorber designed to reduce spring oscillations.
direct-acting telescopic type
A shock absorber designed to reduce spring oscillations.
directional and asymmetric tread patterns
A tread pattern that is both directional and asymmetric, which means the tire is designed to rotate in only one direction and has one side that must face outward to ensure that the tire performs as designed under operating conditions.
directional tread patterns
A tread pattern designed to pump water out from under the tire; each tire must be placed in a particular spot on the vehicle.
directional and asymmetric tread pattern
A tread pattern that is both directional and asymmetric, which means the tire is designed to rotate in only one direction and has one side that must face outward to ensure that the tire performs as designed under operating conditions.
directional tread pattern
A tread pattern designed to pump water out from under the tire; each tire must be placed in a particular spot on the vehicle.
disc brakes
A type of brake system that forces stationary brake pads against the outside of a rotating brake rotor.
disc brake pads
Brake pads that consist of a friction material bonded or riveted to a steel backing plate; designed to wear out over time.
disc brake rotor micrometer
A specially designed micrometer used to measure the thickness of a rotor.
discharge reed valves
A flat, spring-loaded valve used as a check valve on the discharge side of a compressor.
discharge reed valve
A flat, spring-loaded valve used as a check valve on the discharge side of a compressor.
dislocation
The displacement of a joint from its normal position; it is caused by an external force stretching the ligaments beyond their elastic limit.
dispersants
Oil additives that keep contaminants held in suspension in the oil, to be removed by the filter or when the oil is changed.
displacement-on-demand
A feature that allows cylinders to be taken off-line when not needed, such as at vehicle cruise.
distributor base plate
A round metal plate near the top of the distributor that is attached to a distributor housing; also called a breaker plate.
distributor cap
The top portion of a distributor, used to make a connection between the spinning rotor and the high-tension leads.
distributor
The part of an ignition system that distributes the spark to the spark plugs in the correct sequence and at the correct time. It includes a distributor cap, rotor, shaft, and usually a switching device.
distributorless ignition systems
An ignition system that does not include a distributor. It uses signals from the crankshaft position sensor and the camshaft position sensor sent to the PCM to determine when to send a signal to the ignition module.
distributorless ignition system
An ignition system that does not include a distributor. It uses signals from the crankshaft position sensor and the camshaft position sensor sent to the PCM to determine when to send a signal to the ignition module.
distributor’s
The part of an ignition system that distributes the spark to the spark plugs in the correct sequence and at the correct time. It includes a distributor cap, rotor, shaft, and usually a switching device.
doping
The introduction of impurities to pure semiconductor materials to provide N- and P-type semiconductors.
double Cardan joint
A type of joint that uses two Cardan joints housed in a short carrier and that reduces the change in velocity of a single Cardan joint by using the second joint to cancel out the changes in velocity of the first joint.
double crimping
Over crimping or recrimping a fitting to keep it from leaking. It normally results in a bigger leak and is not recommended.
double flare
A seal that is made at the end of metal tubing or pipe.
double-clutching
A technique used to shift gears when a nonsynchronized transmission is used. The driver must push the clutch in multiple times to change gears.
double-insulated
Tools or appliances that are designed in such a way that no single failure can result in a dangerous voltage coming into contact with the outer casing of the device.
double-row ball bearing assembly
A single ball bearing assembly using two rows of ball bearings riding in two channels in the races.
down-flow radiator
A radiator that uses cooling tubes that run vertical. This design requires a higher hood profile.
drag
The slowing down of the crankshaft when it strikes the oil in the crankcase.
drag link
A steel or iron rod that transfers movement of the pitman arm to a relay lever.
drain line
A wire included in a harness with one end grounded to reduce interference or noise being induced into the harness.
drawing-in method
A method for replacing wheel studs that uses the lug nut to draw the wheel stud into the hub or flange.
drift punch
A type of punch used to start pushing roll pins to prevent them from spreading.
drill chuck
A device for securely gripping drill bits in a drill.
drill press
A device that incorporates a fixed drill with multiple speeds and an adjustable worktable. It can be free-standing or fixed to a bench.
drill vice
A tool with jaws that can be attached to a drill press table for holding material that is to be drilled.
drivability technicians
A technician who diagnoses and identifies mechanical and electrical faults that affect vehicle performance and emissions.
drivability technician
A technician who diagnoses and identifies mechanical and electrical faults that affect vehicle performance and emissions.
drive axle assembly
The components that make up the drive axle including the axles, final drive assembly, bearings, and axle housing.
drive axles
An axle that provides power to a wheel.
drive cycle
The operating range of an engine from start-up until shutdown when finished performing its job.
drive line angularity
The relationship of the driveshaft to the component that the driveshaft attaches, measured in degrees of angle.
drive pulley
Any belt-driven pulley used to power an accessory such as power steering or the air-conditioning compressor.
drive shaft
The hollow tube with flexible joints on each end that transmits power from the transmission to the final drive unit.
drive train
A term used to identify the engine, transmission/transaxle, differential, axles, and wheels.
drive axle
An axle that provides power to a wheel.
driveline vibrations
Rotational fluctuations caused by out-of-balance, misaligned, worn, or bent driveline components.
driven center plate
The friction disc that is held firmly against the flywheel by a pressure plate and transfers power from the flywheel to the transmission input shaft.
driving thrust
The force transferred from the tire contact patch through the axle housing and front half of the spring to the fixed shackle point that pushes the vehicle along the road.
drop center
A wheel design with part of the center section of the wheel a smaller diameter than the rest. It is used for mounting and demounting the tire.
dropcenter
A wheel design with part of the center section of the wheel a smaller diameter than the rest. It is used for mounting and demounting the tire.
drum brake micrometer
A tool used for measuring the inside diameter of the brake drum.
drum brake
A type of brake system that forces brake shoes against the inside of a brake drum.
drum brakes
A type of brake system that forces brake shoes against the inside of a brake drum.
drum-style parking brake
A mechanically operated drum brake that can be set while the vehicle is not moving to serve as a parking brake.
dry flanged sleeve
A metal cylinder with a flange embedded into the block pressed into an engine cylinder to give it a new wear surface. The flanged sleeve is held in by the cylinder head.
dry sleeve
A metal cylinder that is pressed into an engine cylinder block that does not come in direct contact with coolant. It is held in place with an interference fit.
dual overhead cam (DOHC) engine
An engine design that is like the overhead cam engine but with two camshafts used per cylinder head; one operates the intake valves and the other operates the exhaust valves.
dual overhead cam (DOHC)
An engine design that is like the overhead cam engine but with two camshafts used per cylinder head; one operates the intake valves and the other operates the exhaust valves.
dual-clutch transmissions
A type of automatically shifting manual transmission in which two separate input shafts are connected to their own clutch. Shifting of the gears alternates between the two input shafts.
dual-clutch transmission
A type of automatically shifting manual transmission in which two separate input shafts are connected to their own clutch. Shifting of the gears alternates between the two input shafts.
dual-drive air-conditioning compressors
An air compressor drive used on some hybrid vehicles. The compressor can be driven by the accessory belt or by an electric motor.
dual-drive air-conditioning compressor
An air compressor drive used on some hybrid vehicles. The compressor can be driven by the accessory belt or by an electric motor.
dual-fuel system
A system that allows an engine to burn two fuels at one time.
dual-fuel
A system that allows an engine to burn two fuels at one time.
dual-mass flywheel (DMF)
A type of flywheel that eliminates excessive transmission gear rattle, reduces gear change/shift effort, and increases fuel economy.
duo-servo drum brake systems
A system that uses servo action in both the forward and reverse direction.
duo-servo drum brake system
A system that uses servo action in both the forward and reverse direction.
duration
The amount of time the valve stays open, given in degrees of rotation of the crankshaft.
duty cycle
Another term for pulse-width modulation.
dwell angle
The amount of time that the primary circuit is energized, measured in degrees of distributor rotation.
dwell control section
Part of the ignition control circuit that determines when the primary circuit will be switched on and for how long current will flow in the primary winding. The dwell period can be varied according to engine speed, improving coil efficiency.
dynamic imbalance
A tire imbalance that causes the wheel assembly to turn inward and outward with each half revolution.
E
E85
A fuel with 85% ethanol and 15% gasoline blend.
ear protection
Protective gear worn when the sound levels exceed 85 decibels, when working around operating machinery for any period of time, or when the equipment you are using produces loud noise.
edge code
A code printed on the edge of a friction lining that describes its coefficient of friction.
effective stroke
The duration of plunger stroke with the spill port covered, which determines the amount of fuel injected.
EGR system monitor
A control module diagnostic test that is run to ensure that the EGR valve and passageways are operating properly.
EGR valve
A valve that connects the exhaust port, or manifold, and the intake manifold. If engine operating conditions are likely to produce oxides of nitrogen, the EGR valve opens, letting some burned exhaust gases pass from the exhaust into the intake system.
EH2 rim
The specialized rim design that is used with some run-flat tires.
elasticity
The amount of stretch or give a material has.
electric solenoid
An electrically operated valve, which in brake systems is used to control the flow of brake fluid in the hydraulic system.
electric braking system
A braking system used to provide braking to trailers; the drum brakes are electrically activated in the trailer when the driver applies the brakes on the towing vehicle.
electric machine
Another name for a traction motor with regenerative capability.
electric power steering (EPS) system
A steering system that uses an electric motor and sensors to provide feedback to the vehicle’s computer systems to decrease steering effort.
electric servos
An air-conditioning door actuator controlled by electricity.
electric servo motors
Also referred to as an electric actuator, a motor that provides movement to operate the air doors in an air box to control air temperature and air movement.
electric power steering system (EPS)
A steering system that uses an electric motor and sensors to provide feedback to the vehicle’s computer systems to decrease steering effort.
electric servo motor
Also referred to as an electric actuator, a motor that provides movement to operate the air doors in an air box to control air temperature and air movement.
electric servo
An air-conditioning door actuator controlled by electricity.
electric solenoids
An electrically operated valve, which in brake systems is used to control the flow of brake fluid in the hydraulic system.
electrical capacity
The ability of a circuit or component to carry electrical loads.
electrical power
A measurement of the rate at which electricity is consumed or created.
electrical resistance
A material’s property that slows down the flow of electrical current.
electrical technicians
A technician who diagnoses, replaces, maintains, identifies fault with, and repairs electrical wiring and computer-based equipment in vehicles.
electrical technician
A technician who diagnoses, replaces, maintains, identifies fault with, and repairs electrical wiring and computer-based equipment in vehicles.
electrically assisted steering (EAS)
A power assist system that uses an electric motor to replace the hydraulic pump to decrease steering effort.
electrically powered hydraulic steering (EPHS)
A steering system that uses an electric motor to produce hydraulic assist for steering.
electro-chemical device
A device such as a battery or fuel cell that uses two forms of energy.
electrohydraulic braking (EHB)
A hydraulic braking system that uses an electrically driven hydraulic pump to pressurize fluid for use in the master cylinder.
electrolysis
The process of pulling metals apart by using electricity or by creating electricity through the use of chemicals and dissimilar metals.
electrolyte
A mixture of water and acid that contains free ions that make it electrically conductive.
electrolyte (batteries)
The liquid in lead-acid battery cells. It is a mixture of about 67% water and 33% sulfuric acid.
electromagnet
A conductor wound in a coil that produces a magnetic field when current flows through it.
electromagnetic clutch arrangement
An arrangement used in hybrid air-conditioning systems to drive the compressor. The air-conditioning clutch is an electromagnetic clutch that works by creating a strong magnetic field that pulls the clutch into mesh with the pulley on the air compressor.
electromagnetic induction
The production of an electrical current in a conductor when it moves through a magnetic field or a magnetic field moves past it.
electromotive force
An electrical pressure or voltage.
electromotive force (EMF)
An electrical pressure or voltage.
electron theory
The theory that electrons, being negatively charged, repel other electrons and are attracted to positively charged objects; thus electrons flow from negative to positive.
electronic brake control (EBC) systems
A hydraulic brake system that has integrated electronic components for the purpose of closely controlling hydraulic pressure in the brake system.
electronic stability control (ESC) system
A computer-controlled system added to ABS and TCS to assist the driver in maintaining vehicle stability while steering.
electronic control module (ECM)
A computer that receives signals from input sensors, compares that information with preloaded software, and sends an appropriate command signal to output devices; used to manage the anti-lock brake system (ABS).
electronic brake control module (EBCM)
The module that controls and monitors the anti-lock braking system.
electronic continuously variable transmission (ECVT)
A type of hybrid transmission that often uses two electric motors in combination with an ICE.
electronic control unit (ECU)
A computer that controls the ignition and fuel control and emissions control systems on an engine; also called the engine control module (ECM) or power train control module (PCM).
electronic control unit (ECU) (heating and cooling system)
When referring to the HVAC system, the electronic module that makes the “decisions” of the climate control system settings based on input sensors and the module programming.
electronic diesel control (EDC)
A computer or electronic control unit that controls diesel fuel injection systems.
electronic fuel injection (EFI)
An injection system in which fuel delivery is controlled electronically, allowing continuous adjustments to the air–fuel ratio.
electronic ignition systems
An ignition system that uses a nonmechanical (electronic) method of triggering the ignition coil’s primary circuit.
electronic ignition system—distributor type
An ignition system that uses a distributor but replaces the contact points with an electronic triggering device.
electronic pressure control (EPC) solenoid
A pulse width–modulated solenoid used to control transmission line pressure in an automatic transmission.
electronic reverse lockout
An electronic solenoid used to prevent accidental engagement into reverse gear while the vehicle is moving forward.
electronic brake control (EBC) system
A hydraulic brake system that has integrated electronic components for the purpose of closely controlling hydraulic pressure in the brake system.
electronically controlled throttle
A system that uses electronic, instead of mechanical, signals to control the throttle. Sometimes called drive-by-wire.
element
The replaceable portion of a filter, such as an air filter element or oil filter element.
emission analyzers
A service bay or lab device used for detecting/measuring vehicle emissions.
emission control systems
A system of devices that are designed to control or reduce harmful gases released to the atmosphere.
emission standards
Cutoff points set by governmental agencies to limit tailpipe emissions.
emission control system
A system of devices that are designed to control or reduce harmful gases released to the atmosphere.
emission
A gas that is released to the atmosphere; usually refers to a harmful gas.
emissions
A gas that is released to the atmosphere; usually refers to a harmful gas.
enameled copper wire
Wire that uses a thin layer of enamel as insulating material. The thinness of the insulation allows the wire to be closely wound in a coil, creating a dense magnetic field when current flows through it.
end play
Referring to the fore and aft movement of the component.
end play (manual transmission)
Unwanted lateral movements of the worm shaft.
end play (transmission)
Referring to the fore and aft movement of the component.
end play (wheels)
The in-and-out movement of the hub caused by clearance within the wheel bearing assembly.
Energy Policy Act (EPAct92)
Regulations enacted in 1992 by the US Congress to promote the use of alternative fuel vehicles and fuels.
energy
The ability to do work.
engine control module (ECM)
A computer that controls the ignition and fuel control and emissions control systems on an engine; also the electronic control unit (ECU) or power train control module (PCM).
engine balancer
An expansive bench unit complete with computer controls, a lathe and drill press for machining metal for the balancing procedure, and all necessary adapters for most applications of crankshaft assemblies.
engine bearings
A specially designed metal piece that supports circular moving parts.
engine block’s deck
The portion of the engine cylinder block on which the head gasket lies on and to which the cylinder head is bolted.
engine block dowel pinhole
The hole where the engine cylinder block dowel pins are fixed.
engine configuration
The way engine cylinders are arranged—for example, V, flat, or in-line.
engine coolant temperature (ECT) sensor
A sensor that changes resistance based upon coolant temperature; also known as a thermistor.
engine coolant temperature sensor
A thermistor that measures the temperature of the engine coolant.
engine displacement
The size of the engine given in cubic inches, cubic centimeters, and liters. It is found by multiplying the piston displacement by the number of cylinders the engine has. Sometimes called “swept volume.”
engine hoists
A small crane used to lift engines.
W
W engine
A term used to describe an engine configuration consisting of two VR cylinder banks in a deep V arrangement.
E
engine bearing
A specially designed metal piece that supports circular moving parts.
engine block deck
The portion of the engine cylinder block on which the head gasket lies on and to which the cylinder head is bolted.
engine hoist
A small crane used to lift engines.
engine-driven hydraulic pump
A power steering pump driven by a belt or gear off of the crankshaft.
E
Environmental Protection Agency (EPA)
Federal government agency that deals with issues related to environmental safety.
epitrochoid curve
The circular movement around the perimeter of another circle. This is the movement that the rotary engine uses to ensure that the rotor stays in contact with the housing.
ethanol
Alcohol-based motor fuel made from starches and sugars.
ethylene glycol
A chemical used as anti-freeze that provides the lower freezing point of coolant and raises the boiling point. It is a toxic anti-freeze.
evaporative emission (EVAP) system
A system used to capture vapors or gases from an evaporating liquid.
evaporator temperature sensor
A thermistor that reads the temperature of the evaporator, used to ensure that the evaporator does not freeze.
evaporator
The air-conditioning component normally located in the passenger compartment designed to allow low-pressure refrigerant liquid to change states to a gas.
event cylinder
The cylinder that uses the spark to ignite the air–fuel mixture on a waste spark ignition system.
exhaust brake
A brake system that restricts the flow of exhaust gases through the engine by closing a butterfly valve located in the exhaust manifold. Restricting the exhaust flow causes the engine speed to slow down, slowing the vehicle.
exhaust gas recirculation (EGR) system
A system that recirculates a portion of burned gases back into the combustion chamber to displace air and fuel and cool combustion temperatures.
exhaust gas recirculation (EGR) valve
A valve that allows a controlled amount of exhaust gas into the intake manifold during a certain period of engine operation. Used to lower nitrogen oxide exhaust emissions.
exhaust stroke
The stroke in an engine cycle when the piston moves up, with the exhaust valve(s) open, exhausting the burned exhaust gases out through the exhaust system.
exhaust valves
The valve through which exhaust gases are forced out of the combustion chamber.
exhaust valve
The valve through which exhaust gases are forced out of the combustion chamber.
expander
The part of an oil control ring that holds the ring against the cylinder wall.
expansion volume
An engineered space that allows for growth of the volume of a liquid as it heats and expands.
Extended Mobility Technology (EMT)
Tires with thick sidewalls that allow the tire to be driven on even when it has no air pressure.
extension housing
A component of the automatic transmission housing that covers the output shaft of the transmission. The extension housing also supports the end of the driveshaft and may hold components such as the vehicle speed sensor, speedometer drive assembly, and governor assembly.
external bleeding
The loss of blood from an external wound; blood can be seen escaping.
external combustion engine
An engine that runs on heat applied externally to the cylinder. For example: the steam engine.
external drive shafts
A shaft used to transfer power from the transmission to the live axle.
external drive shaft
A shaft used to transfer power from the transmission to the live axle.
externally equalized valve
A style of TXV where the external valve uses the sensing bulb on the outlet side to overcome spring pressure to open the valve.
extreme loading
Large pressure placed on two bearing surfaces. Extreme loading will try to press oil from between bearing surfaces.
extreme-pressure additives
An oil additive that ensures that a protective coating is given to moving engine parts and that keeps oil from being forced out under extreme pressure. Helps oil to cushion components.
extreme-pressure additive
An oil additive that ensures that a protective coating is given to moving engine parts and that keeps oil from being forced out under extreme pressure. Helps oil to cushion components.
eye ring terminals
A type of crimp or solder terminal that has an enclosed eyelet to connect the terminal with a bolt or screw.
eye ring terminal
A type of crimp or solder terminal that has an enclosed eyelet to connect the terminal with a bolt or screw.
F
fast chargers
A type of battery charger that charges batteries quickly.
fasteners
Devices that securely hold items together, such as screws, cotter pins, rivets, and bolts.
fault codes
An alphanumeric code system used to identify potential problems in a vehicle system.
fault
A code set by the computer indicating system or component malfunction.
faults
A code set by the computer indicating system or component malfunction.
feedback signal
A voltage signal sent back to an electronic control unit. The feedback signal is how the control module is able to interpret temperature or other information from its sensors.
feedback system
A system that uses feedback to adjust what it is doing. Typically, a module gives a command and waits to see if the command was followed by use of a sensor.
feeler gauges
A thin blade device for measuring space between two objects.
feeler gauge
A thin blade device for measuring space between two objects.
ferrous metal
Metals that have an iron compound in their makeup or that are magnetic.
ferrous metals
Metals that have an iron compound in their makeup or that are magnetic.
fiber optics
Fine glass fibers through which light is transmitted.
fill plug
Usually a threaded plug that can be removed to allow the level of a fluid to be checked and filled. This could also be a rubber snap fit plug.
fillet area
The area of the crankshaft that meets up with the rod bearing journal or main bearing journal.
fillet
The radius portion of an inside corner that reduces stress at the corner.
fillets
The radius portion of an inside corner that reduces stress at the corner.
filter media
A screen designed to keep debris from the TXV that is normally located in the receiver dryer.
filter sock
The first line of defense in the fuel supply system. The sock typically consists of a fine mesh, which prevents most small particles from being drawn into the fuel pump and sent through the rest of the fuel system.
fin
A small, flat piece of metal placed between the tubes to help with the transfer of heat from the coolant to the air, refrigerant to air, or air to refrigerant. The metal heats up due to contact with the hot pipes in the case of a radiator or heater core and from hot air in the case of an evaporator.
final drive assembly
An assembly used to power the drive wheels and allow the wheels to rotate at different speeds as the vehicle turns.
final drive
A component that provides a final gear reduction and allows for the difference in speed of each wheel when cornering.
fine (UNF)
Used to describe thread pitch; it stands for Unified National Fine.
finished rivet
A rivet after the completion of the riveting process.
fins
A small, flat piece of metal placed between the tubes to help with the transfer of heat from the coolant to the air, refrigerant to air, or air to refrigerant. The metal heats up due to contact with the hot pipes in the case of a radiator or heater core and from hot air in the case of an evaporator.
fire rings
Steel rings integrated into the cylinder head gasket nearest the combustion chambers that provide extra sealing to seal in the high combustion pressures.
firing line
The tall lines on a parade pattern that indicate the voltage required to initially jump the spark plug gap.
first aid
The immediate care given to an injured or suddenly ill person.
first-degree burns
Burns that show reddening of the skin and damage to the outer layer of skin only.
five-gas analyzer
A tool that uses sensors to measure the level of gases in the exhaust stream.
fixed calipers
A type of brake caliper bolted firmly to the steering knuckle or axle housing, having at least one piston on both sides of the rotor.
fixed orifice tube system
A system with a fixed orifice tube that uses an accumulator between the evaporator and the compressor.
fixed resistors
A resistor that has a fixed value.
fixed orifice
A system in which a hole of a predetermined size is used as a means of pulling crankcase vapors into the intake manifold to be burned.
fixed caliper
A type of brake caliper bolted firmly to the steering knuckle or axle housing, having at least one piston on both sides of the rotor.
fixed resistor
A resistor that has a fixed value.
fixed-orifice PCV system
A system in which a hole of a predetermined size is used as a means of pulling crankcase vapors into the intake manifold to be burned.
fixed-type joint
A joint that does not slide to allow for shaft lengthening or shortening; it simply allows for angle changes as the suspension moves.
flame front
The front edge of the burning air/fuel mixture in the combustion chamber.
flame propagation
The movement of the flame through the combustion chamber during the combustion process.
flame spread
The phase of combustion in which there is a sharp pressure rise in the combustion chamber because of the sudden combustion of the fuel.
flare nut wrench
A type of box-end wrench that has a slot in the box section to allow the wrench to slip through a tube or pipe. Also called a flare tubing wrench.
flashback arrestors
A spring-loaded valve installed on oxyacetylene torches as a safety device to prevent flame from entering the torch hoses.
flashback arrestor
A spring-loaded valve installed on oxyacetylene torches as a safety device to prevent flame from entering the torch hoses.
flasher can
A mechanism that turns the vehicle’s turn signal and hazard flasher bulbs on and off.
flat blade screwdriver
A type of screwdriver that fits a straight slot in screws.
flat seat with washer
A type of lug nut that is flat where it bolts to the wheel and has a washer affixed that allows it to turn independent of the hex part of the lug nut.
flat seat without washer
A type of lug nut that is flat where it bolts to the wheel.
flat tappet
A camshaft specifically designed to push on flat bottom lifters (nonroller types). It typically has a higher rolling resistance than the rollerstyle camshafts.
flat-nosed pliers
Pliers that are flat and square at the end of the nose.
flathead engines
An L-head engine with valves in the block.
flathead engine
An L-head engine with valves in the block.
flex hone
A machine tool with abrasive stones that is used to refinish the inside of the cylinder walls.
flex plate
A metal part attached to the rear of the crankshaft that connects to the torque converter in a vehicle with an automatic transmission.
flexible-fuel vehicles (FFVs)
A vehicle than can operate on two different fuels blended together in various mixture amounts by percentage.
flexible-fuel vehicle (FFV)
A vehicle than can operate on two different fuels blended together in various mixture amounts by percentage.
float chamber
A chamber that holds a quantity of fuel at atmospheric pressure ready for use.
float-type fuel gauge
A system for determining the level of liquid fuel in a tank using a float and potentiometer.
floating pin
A round metal pin that has a very small clearance but is free to float in the piston and connecting rod.
flow-control valve
A valve used in power steering pumps to control the amount of flow out of the power steering pump.
fluid coupler
A type of hydraulic coupling used on vintage vehicles to connect and transfer power from the engine to the transmission.
fluid dissipater
A silicone fluid component that allows the mass of a fluid type harmonic balancer to rotate at a more constant speed than the crankshaft to help even out the torsional vibrations of the crankshaft.
flux
A liquid or paste that protects a soldering or welding joint from oxidization.
flywheel ring gear
Large, round, externally toothed gear that is usually press-fit to the outer diameter of the flywheel and used along with the starter to crank the engine over.
flywheel
The heavy, circular flat plate that keeps the engine rotating when power is not produced, such as on the exhaust, intake, and compression strokes.
force
The effort to produce a push or pull action.
forced induction
The pressurization of airflow going into the cylinder through the use of a turbocharger or supercharger.
forces capability map data
Data preprogrammed into the electronic control unit’s memory by the manufacturer and used to determine how much power assistance is needed based on input from the vehicle’s speed sensor and steering sensor.
forcing screw
The center screw on a gear, bearing, or pulley puller. Also called a jacking screw.
forged connecting rods
A strong metal connecting rod hammered into shape by large presses used to connect the piston to the crankshaft.
forged connecting rod
A strong metal connecting rod hammered into shape by large presses used to connect the piston to the crankshaft.
four-post hoist
A type of hoist that the vehicle is driven onto that uses two long, narrow platforms to lift the vehicle.
four-stroke engine
An engine that uses four strokes—intake, compression, power, and exhaust—to complete its cycle.
four-stroke
An engine that uses four strokes—intake, compression, power, and exhaust—to complete its cycle.
four-wheel drive (4WD)
A drive train layout in which the engine drive has either two wheels or four wheels depending on which mode is selected by the driver.
four-wheel steering system
A steering system in which the front wheels are controlled normally and the rear wheels use a computer and electric motors to turn the rear linkage.
four-wheel steering
A steering system in which the front wheels are controlled normally and the rear wheels use a computer and electric motors to turn the rear linkage.
fracture split
A method used on powdered metal connecting rods where the big end of the connecting rod is broken in half and can be identified by a ragged finish of the big end’s parting surfaces.
free electrons
An electron located on the outer ring, called the valence ring, that is only loosely held by the nucleus and that is free to move from one atom to another when an electrical potential (pressure) is applied.
free electron
An electron located on the outer ring, called the valence ring, that is only loosely held by the nucleus and that is free to move from one atom to another when an electrical potential (pressure) is applied.
free play
The amount of movement between two mating parts.
free-play
The amount of movement between two mating parts.
freewheeling engine
An engine that has enough clearance between the piston and the valves so that in the event the timing belt or chain breaks, the valves that are hanging all the way open will not contact the piston, thus preventing engine damage.
freeze-frame
A feature of OBDII that records events before, during, and after a fault occurs.
frequency
The rate of change in direction, oscillation, or cycles in a given time.
friction
The resistance created by surfaces in contact. Kinetic friction is resistance to motion when one surface moves over another. Static friction is resistance to motion between two surfaces that are not moving.
friction bearing
A bearing that uses sliding motion between components, such as a clutch pilot bushing.
friction facings
The material riveted to each side of the clutch disc that mates to the flywheel and pressure plate. Used to provide friction and a wear surface for the clutch assembly.
friction facing
The material riveted to each side of the clutch disc that mates to the flywheel and pressure plate. Used to provide friction and a wear surface for the clutch assembly.
front bearing retainer
The housing that bolts the input shaft bearing in place on the front of the transmission.
front hydraulic pump
A hydraulic pump used to supply lubrication oil and hydraulic pressure to the different components inside the automatic transmission.
front-wheel drive (FWD)
A drive train layout in which the engine drives the front wheels.
fuel filler neck
The upper end of the fuel filler tube leading down to the fuel tank, which accepts the fuel hose nozzle at the gas station pump.
fuel cell
An electro-chemical device that uses hydrogen and oxygen to create electricity.
fuel cell (electric) vehicle (FCV)
A vehicle that converts fuel to electricity in a direct electrochemical process, with more energy extracted from the fuel source than in traditional internal combustion engines.
fuel composition sensor
A device that measures the percentage of alcohol in gasoline.
fuel filter
A device that removes impurities (dirt and water) from the fuel before they reach the carburetor or injection system. Filters may be made of metal or plastic screen, paper, or gauze.
fuel metering system
Equipment in a motor vehicle that delivers the proper amount of fuel to each cylinder.
fuel methanol
A toxic alcohol fuel.
fuel pressure regulator
A system that controls the pressure of fuel entering the injectors.
fuel pumps
A mechanically or electrically driven vacuum device used to draw fuel from the tank and force it into the fuel system.
fuel pump relay
A relay to turn on or off the high-amperage circuit of the fuel pump.
fuel rail
Tubing that connects several injectors to the main fuel line.
fuel shutoff mode
A safety precaution by which fuel is shut off when certain conditions are met during a vehicle crash.
fuel supply system
Equipment in a motor vehicle that delivers fuel to the engine.
fuel system
Equipment in a motor vehicle that delivers fuel to the engine.
fuel tank pressure sensor
A sensitive pressure sensor mounted in the fuel tank or EVAP system used to monitor the system for leaks.
fuel systems
Equipment in a motor vehicle that delivers fuel to the engine.
fuel pump
A mechanically or electrically driven vacuum device used to draw fuel from the tank and force it into the fuel system.
fulcrum
The point around which a lever rotates and that supports the lever and the load.
fulcrum rings
A steel ring that is used as a pivot point for the diaphragm spring in the pressure plate.
fulcrum ring
A steel ring that is used as a pivot point for the diaphragm spring in the pressure plate.
full floating axle
An axle that does not support any weight; if removed, the vehicle will still roll on its wheels.
full frame construction
Construction of the frame using a heavy steel channel iron or boxed steel. The frame runs from the front of the vehicle to the rear as one solid piece, and the body of the vehicle attaches to this part by bolts and rubber body mounts.
full-flow filters
An oil filter installed on production cars. This oil filter cleans all oil coming from the oil pump on its way to the lubricated components.
full-flow filter
An oil filter installed on production cars. This oil filter cleans all oil coming from the oil pump on its way to the lubricated components.
full-frame construction
Construction of the frame using a heavy steel channel iron or boxed steel. The frame runs from the front of the vehicle to the rear as one solid piece, and the body of the vehicle attaches to this part by bolts and rubber body mounts.
fuse
A safety device that self-destructs to prevent excessive current flowing in a circuit in the event of a fault.
fuses
A safety device that self-destructs to prevent excessive current flowing in a circuit in the event of a fault.
G
galleries
Passageways drilled or cast into the engine block or head(s), which carry pressurized lubricating oil to various moving parts in the engine, such as the camshaft bearings.
gallium-arsenide
A semiconductor used in high-frequency circuits.
garter spring
A coiled spring that is fitted to the inside of the sealing lip of many seals, used to hold the lip in contact with the shaft.
garter spring lip seals
A seal that has a spring to maintain pressure on the seal’s surface to prevent leakage.
garter spring lip seal
A seal that has a spring to maintain pressure on the seal’s surface to prevent leakage.
gas direct injection (GDI) cylinder head
A cylinder head designed to accept a gasoline injector directly in the combustion chamber instead of in the intake manifold.
gas welding goggles
Protective gear designed for gas welding; they provide protection against foreign particles entering the eye and are tinted to reduce the glare of the welding flame.
gasket
A rubber, cork, or paper spacer that goes between two parts to seal the gap between the parts.
gasket scraper
A broad sharp flat blade to assist in removing gaskets and glue.
gaskets
A rubber, cork, or paper spacer that goes between two parts to seal the gap between the parts.
gasoline
A volatile, flammable liquid mixture of hydrocarbons, obtained from crude oil and used as fuel for internal combustion engines.
gasoline direct injection (GDI)
A fuel injection system in which fuel is sprayed directly into the combustion chamber.
gassing
The escape of gas from the battery.
gauge sending unit
A device used for transmitting a signal to control a fuel gauge.
gear lube
A type of lubricant primarily used to lubricate transmission and differential gears but also used to lubricate some wheel bearings.
gear pullers
A tool with two or more legs and a cross bar with a center forcing screw to remove gears.
gear pumps
A type of front pump used on some vehicles that uses two rotating gears to force fluid out of the pump.
gear ratio
The ratio of the number of turns that a drive gear must complete to turn the driven gear one turn. Typically this is a calculation of the driven gear to the drive gear. Ratios are listed, for example, as 2:1 or 4.3:1.
gear reduction
The use of a small gear to drive a large gear. The result is in an increase in torque but a decrease in speed.
gear set
Two or more gears that are in mesh with each other.
gear shift lever
The lever that the driver uses to shift the transmission.
gear synchronizer
An assembly in the transmission that is used to bring two unequally spinning shafts or gears to the same speed when upshifting or downshifting.
gear pump
A type of front pump used on some vehicles that uses two rotating gears to force fluid out of the pump.
gear
A relatively round, rotating part with internal or external teeth that are designed to mesh with another gear for the purpose of transmitting torque.
gear ratios
The ratio of the number of turns that a drive gear must complete to turn the driven gear one turn. Typically this is a calculation of the driven gear to the drive gear. Ratios are listed, for example, as 2:1 or 4.3:1.
geared oil pump
An oil pump that has two gears running side by side together to move oil from one side of the pump gears to the other.
gears
A relatively round, rotating part with internal or external teeth that are designed to mesh with another gear for the purpose of transmitting torque.
gelling
A thickening effect of oil in cold weather. This is not a desirable trait for lubricating oil, as it will not flow when it is gelling. Wax content in base stock mineral oil makes gelling worse.
germanium
A type of semiconductor.
girdle
A metal device connected to the bottom of the engine cylinder block to create strength for the main bearing caps.
governor
A mechanical device that creates a pressure using centrifugal force. The pressure is proportional to vehicle speed.
governor pressure
The pressure created by the governor, which is used to make the shift valves upshift and is proportional to vehicle speed.
gradient resistance
Resistance encountered when a vehicle travels up a hill, requiring torque to be applied to overcome it.
gravity pouring
The casting process used for creating metal parts.
grease
A lubricating liquid thickened to make it suitable for use with many wheel bearings.
grease seal
A component that is designed to keep grease from leaking out and contaminants from leaking in.
grinding wheels and discs
Abrasive wheels or flat discs fitted to bench, pedestal, and portable grinders.
ground
The return path for electrical current in a vehicle chassis, other metal of the vehicle, or dedicated wire.
grounds
Fault conditions in a circuit where the circuit is unintentionally contacting a grounded component or wire. This may result in a short, in the case of a power wire, or it could cause a circuit to stay live in the case of a switched ground circuit.
guide pins
Pins that allow the caliper to move in and out as the brakes operate and as the brake pads wear.
H
half-shaft
An axle that has CV joints on each end and that fits between the transaxle and wheel. Typically, one is used on each side of a vehicle.
half-shafts
An axle that has CV joints on each end and that fits between the transaxle and wheel. Typically, one is used on each side of a vehicle.
Hall effect
An electrical effect where electrons tend to flow on one side of a special material when exposed to a magnetic field, causing a difference in voltage across the special material. When the magnetic fields is removed, the electrons flow normally and there is no difference of voltage across the special material. This effect can be used to determine the position or speed of an object.
Hall-effect
An electrical effect where electrons tend to flow on one side of a special material when exposed to a magnetic field, causing a difference in voltage across the special material. When the magnetic field is removed, the electrons flow normally and there is no difference of voltage across the special material. This effect can be used to determine the position or speed of an object.
Hall-effect switch
The portion of an electronic ignition system used to trigger the ignition system. Hall-effect switches operate by using a potential difference, or voltage, created when a current-carrying conductor is exposed to a magnetic field. If a magnetic field is applied at right angles to the direction of current flow in a conductor, the lines of magnetic force permeate the conductor, and the electrons flowing in the conductor are deflected to one side. This deflection creates a potential difference across the conductor. The stronger the magnetic field, the higher the voltage.
halogen lamps
A type of bulb that produces a bright white light.
halogen lamp
A type of bulb that produces a bright white light.
hard rubber mallet
A special-purpose tool with a head made of hard rubber; often used for moving things into place where it is important not to damage the item being moved.
hard shifting
A shifting problem in which the shifter will not move smoothly into the desired gear, requiring excessive force by the driver to set it into gear.
hardened seats
A valve seat that has undergone a heat-treating process to become more robust and capable of withstanding the severe demands of today’s vehicles and drivers.
hardened seat
A valve seat that has undergone a heat-treating process to become more robust and capable of withstanding the severe demands of today’s vehicles and drivers.
harmonic balancer
A round metal disc connected to the front of the crankshaft that smoothes out torsional vibrations created by the crankshaft.
hatchback
A round metal disc connected to the front of the crankshaft that smoothes out torsional vibrations created by the crankshaft.
hatchbacks
A vehicle that has a shared passenger and cargo area; it typically is available in three- and five-door arrangements.
hazard
Anything that could hurt you or someone else.
hazardous environment
A place where hazards exist.
hazardous material
Any material that poses an unreasonable risk of damage or injury to persons, property, or the environment if it is not properly controlled during handling, storage, manufacture, processing, packaging, use and disposal, or transportation.
head gasket
A thin piece of material, often a multilayered, bimetallic sheet used to seal the cylinder head assembly to the engine block.
header
A specially tuned exhaust manifold typically made of exhaust pipes. These pipes are usually made equal length to ensure equal flow between cylinders.
headgear
Protective gear that includes items like hairnets, caps, or hard hats.
heat fade
Brake fade caused by the buildup of heat in braking surfaces, which get so hot they cannot create any additional heat, leading to a loss of friction.
heat buildup
A dangerous condition that occurs when the glove can no longer absorb or reflect heat and heat is transferred to the inside of the glove.
heat dissipation
The spreading of heat over a large area to increase heat transfer.
heat range
The rating of a spark plug’s operating temperature.
heat transfer
The flow of heat from a hotter part to a cooler part; it can occur in solids, liquids, or gases.
heated air intake system
A system that uses hot air from around the exhaust manifold to warm the air going into the intake manifold.
heated diode
A sniffer that uses electricity to determine if there is a refrigerant leak; considered the best sniffer for R-134a.
heater control cables
Cables that control the air doors in an air box as part of the air distribution system.
heater core
A heat-exchanging device that transfers heat converted by the fuel burning in the engine to the passenger compartment.
heavy line technicians
A technician who undertakes major engine, transmission, and differential overhaul and repair.
heavy line technician
A technician who undertakes major engine, transmission, and differential overhaul and repair.
helical gears
Gears that have teeth set on an angle to the gear face; they operate more quietly than spur gears.
helical-cut gears
A type of gear in which the teeth are cut in a spiral down the axis of the gear.
helical-cut gear
A type of gear in which the teeth are cut in a spiral down the axis of the gear.
helical-geared limited slip differential
A type of differential that responds very quickly to changes in traction and that does not bind from friction in turns or lose its effectiveness since there are no clutches.
helical-geared limited slip differentials
A type of differential that responds very quickly to changes in traction and that does not bind from friction in turns or lose its effectiveness since there are no clutches.
helix
The curve created by a smooth spiral and used in the angle of gear teeth and coil springs.
Helmholtz resonator
A device that uses the principle of noise cancellation through the collision of sound waves. When necessary, the resonator is used in addition to the muffler to cancel additional sounds. This resonator may also be used on the induction system to muffle noise of airflow through the induction system. It is named after physicist Hermann Von Helmholtz.
hemispherical cylinder head
A combustion chamber that is hemispherical in shape with the valves in a crossflow arrangement and the spark plug near the center of the cylinder head directly over the top of the piston.
hertz
The unit for electrical frequency measurement.
high resistance
A term that describes a circuit or components with more resistance than designed. The resistance of a component or circuit relative to a low resistance. It can also refer to a faulty circuit where a section or component has excess unwanted resistance.
high-intensity discharge (HID)
A type of lighting that produces light with an electric arc rather than a glowing filament.
high-pressure accumulators
A storage container designed to contain high-pressure liquids such as brake fluid.
high-pressure switches
A switch designed to open at a predetermined high pressure to protect the compressor; it is normally located on the high side line near the compressor.
high-pressure accumulator
A storage container designed to contain high-pressure liquids such as brake fluid.
high-pressure switch
A switch designed to open at a predetermined high pressure to protect the compressor; it is normally located on the high side line near the compressor.
high-tension leads
The heavy insulated wires used to connect the distributor cap terminals to the spark plugs, and the ignition coil to the distributor cap, or on waste spark systems, the coils to the spark plugs.
high-tension terminals
The terminals on the coils and distributor cap that the high-tension leads are connected to.
high-tension terminal(s)
The terminals on the coils and distributor cap that the high-tension leads are connected to.
high-voltage spark
The electrical arc that takes place between the center and the side electrode of a spark plug.
history code
A fault code that has occurred but is not current and is saved in the PCM’s memory for 40 drive cycles.
hold function
A setting on a DVOM to store the present reading.
hold-down springs
Springs that hold the brake shoes against the backing plate.
hold-down spring tool
A tool used for removing and installing hold-down springs.
hold-in winding
A low-current winding found in starter solenoids that holds the plunger in the activated position.
hole theory
The theory that as electrons flow from negative to positive, holes flow from positive to negative.
hollow punches
A punch with a center hollow for cutting circles in thin materials such as gaskets.
hollow punch
A punch with a center hollow for cutting circles in thin materials such as gaskets.
honing
The smoothing-out process of the cylinder walls performed after the boring process. This is the final step in refinishing the cylinder; it creates the proper crosshatched pattern necessary for the piston rings to seal and seat into to give the combustion chamber the proper seal.
hooke's joint
A joint that consists of a steel cross with four hardened bearing journals, mounted on needle rollers in hardened caps, which locate the cross in the eyes of the yokes. The cross swivels in the yokes as the drive is transferred across the joint.
horizontally opposed engine
An engine with two banks of cylinders, 180 degrees apart, on opposite sides of the crankshaft. It is also called a flat engine or a boxer engine.
horizontally opposed engines
An engine with two banks of cylinders, 180 degrees apart, on opposite sides of the crankshaft. It is also called a flat engine or a boxer engine.
horsepower
An amount of work performed in a given time.
hoses
Flexible lines used to direct liquids or gases.
hot junction
The heating point of a thermocouple.
hybrid drive system
A drive system that uses two or more propulsion systems such as electric motors and an ICE.
hybrid electric vehicles (HEVs)
A vehicle that uses two power sources for propulsion, one of which is electricity.
hybrid electric vehicle (HEV)
A vehicle that uses two power sources for propulsion, one of which is electricity.
hydraulic control unit (HCU)
An assembly that houses electrically operated solenoid valves used in electronic braking systems; also called a modulator.
hydraulic fade
Brake fade caused by boiling brake fluid.
hydraulic press method
A method for replacing wheel studs that uses a press to force the wheel stud into the flange until it bottoms out.
hydraulic actuators
A hydraulically controlled cylinder that engages or disengages the clutch pedal.
hydraulic jacks
A type of vehicle jack that uses oil under pressure to lift vehicles.
hydraulic pressure test
The use of a hydraulic pressure gauge to measure the amount of hydraulic pressure produced in each gear range.
hydraulic valve lifter
A small mechanical cylinder with a hydraulically operated internal piston used to automatically take up the slack (valve clearance) in the valve train.
Hydraulic valve lifters
A small mechanical cylinder with a hydraulically operated internal piston used to automatically take up the slack (valve clearance) in the valve train.
hydraulic actuator
A hydraulically controlled cylinder that engages or disengages the clutch pedal.
hydraulic jack
A type of vehicle jack that uses oil under pressure to lift vehicles.
hydraulically actuated electronically controlled unit injector (HEUI)
A diesel fuel injection system that operates by drawing fuel from the tank using a tandem high- and low-pressure fuel pump.
hydro-cracking
A process in which group 2 and group 3 oils are refined with hydrogen at much higher temperatures and pressures. This process results in a base mineral oil with many of the higher performance characteristics of synthetic oils.
hydrocarbon (HC)
An exhaust emission that mixes with nitrogen oxides and sunlight to form ozone (smog) and acid rain. Hydrocarbons result from incomplete combustion.
Hydrocarbons
An exhaust emission that mixes with nitrogen oxides and sunlight to form ozone (smog) and acid rain. Hydrocarbons result from incomplete combustion.
hydrocarbons (HCs)
An exhaust emission that mixes with nitrogen oxides and sunlight to form ozone (smog) and acid rain. Hydrocarbons result from incomplete combustion.
hydrocarbons (HC)
A microscopic unburned fuel particle that contributes to photochemical smog and helps form ground-level ozone.
hydrodynamic seals
Oil seal flutes or swirls that are part of the oil seal and that create a pumping action to return oil to the transmission as the shaft rotates, enabling lubrication.
hydrodynamic seal
Oil seal flutes or swirls that are part of the oil seal and that create a pumping action to return oil to the transmission as the shaft rotates, enabling lubrication.
hydrogenated nitrile butadiene rubber (H-NBR)
A man-made rubber with the same characteristics as NBR but with better resistance to heat.
hydrogenating
A process used during refining of crude oil. Hydrogen is added to crude oil to create a chemical reaction to take out impurities such as sulfur.
hydrometer
A tool that measures the specific gravity of a liquid.
hygroscopic
A property of a substance or liquid that causes it to absorb moisture (water), as a sponge absorbs water. Brake fluid will absorb water out of the air; thus it is hygroscopic.
hypereutectic piston
An aluminum piston that is cast with a 16% to 19% silicon content and that has minimal expansion rates.
hypoid bevel gear
A special design of spiral bevel gear, with the centerline of the pinion below the centerline of the ring gear.
hypoid gears
A type of helical gear used to change the direction of motion 90 degrees. The axis of the input gear does not line up on the centerline of the output gear.
hypoid gear
A type of helical gear used to change the direction of motion 90 degrees. The axis of the input gear does not line up on the centerline of the output gear.
Hypoid bevel gears
A special design of spiral bevel gear, with the centerline of the pinion below the centerline of the ring gear.
I
idle
The speed at which an engine runs without any throttle applied.
idle stop
A feature that turns off the internal combustion engine when the vehicle is at a standstill.
idler gear
A gear used in between two gears to change the direction of the rotation of the driveshaft or drive axles in the transmission.
idling
A condition in which a gear is spinning but not moving.
idling five-gas test
A five-gas analysis test conducted during vehicle idling.
ignition
The burning of the fuel mixture ignited by the heat of compression.
ignition advance
The means of causing the spark to occur earlier within the compression stroke for better performance and fuel economy during changing engine conditions.
ignition coil
A device used to amplify an input voltage into the much higher voltage needed to jump the electrodes of a spark plug.
ignition coil pack
A group of two or more ignition coils housed in one assembly.
ignition control module (ICM)
A general control unit of some electronic ignition systems, usually with current and dwell angle control, driver and output stage, and in some cases, electronic spark timing functions.
ignition delay/lag period
The time it takes for the fuel to ignite after the fuel is injected into the engine.
ignition modules
An electronic component that electronically controls the ignition coil or coils.
ignition switch
A switch operated by a key or start/stop button and used to turn on or off a vehicle’s electrical and ignition system.
ignition delay period
The time it takes for the fuel to ignite after the fuel is injected into the engine.
Ignition coils
A device used to amplify an input voltage into the much higher voltage needed to jump the electrodes of a spark plug.
impact driver
A tool that is struck with a hammer to provide an impact turning force to remove tight fasteners.
in-line engine
An engine in which the cylinders are arranged side by side in a single row.
incandescent lamps
The traditional bulb that uses a heated filament to produce light.
incandescent lamp
The traditional bulb that uses a heated filament to produce light.
included angle
The angle of camber added or subtracted to the SAI angle. This is the angle of the pivot points in relation to the camber angle of the wheel. Also referred to as the diagnostic angle.
independent rear suspension (IRS)
A type of suspension system where each rear wheel is capable of moving independently of the other.
independent rear axle
A type of rear suspension system that allows each wheel on the axle to move independently of the other.
independent suspension
A system for allowing the up-and-down movement of one tire without affecting the other tire on that axle.
independent suspension drive axle
A type of suspension that allows each wheel on a drive axle to move independently of the other.
indirect fuel injection
A fuel injection system in which the fuel is injected into a separate chamber in the cylinder head, often called a prechamber.
indirect TPMS
A type of automated tire pressure monitoring system that uses the anti-lock braking system of a vehicle to measure the difference in the rotational speed of the four wheels to determine tire pressure.
induced voltage
The creation of voltage in a conductor by movement of a magnetic field that is near that conductor.
induction coil
An electrical transformer that uses magnetic fields to produce high-voltage pulses from low-voltage direct current.
induction hardened
A process for hardening metal by touching it to a device that raises the temperature of the part with heat or magnets and then suddenly cooling it in water, oil, or another chemical.
induction hardening
A process for hardening metal by touching it to a device that raises the temperature of the part with heat or magnets and then suddenly cooling it in water, oil, or another chemical.
induction-hardened
A process for hardening metal by touching it to a device that raises the temperature of the part with heat or magnets and then suddenly cooling it in water, oil, or another chemical.
induction-type systems
A type of ignition system that uses a magnetic pulse generator to trigger the spark.
Induction-type systems
A type of ignition system that uses a magnetic pulse generator to trigger the spark.
inductive current
The current that has been created across a conductor by moving it through a magnetic field.
inductive-type sensors
A sensor mounted on the crankcase housing that is used to sense the movement of the ring gear teeth on the flywheel, or a toothed disc on the crank pulley.
inductive-type sensor
A sensor mounted on the crankcase housing that is used to sense the movement of the ring gear teeth on the flywheel, or a toothed disc on the crank pulley.
inert gas
A gas that will not react chemically.
inertia
The resistance to a change in motion.
infrastructure
The system for supplying fuel for transportation use; includes ships, pipelines, trucks, etc.
ingression
The passing of foreign bodies, such as moist warm air, through the air-conditioning lines or fittings.
injector
A valve that is controlled by a solenoid or spring pressure to inject fuel into the engine.
injectors
A valve that is controlled by a solenoid or spring pressure to inject fuel into the engine.
inlet port
Connects the reservoir with the space around the piston and between the piston cups in a brake master cylinder.
inlet reed valve
A flat spring-loaded valve that allows gaseous refrigerant to enter the compressor.
inner race
The inside component of a wheel bearing that has a smooth, hardened surface for rollers or balls to ride on.
inner tie-rod or socket
The inner tie-rod is attached to the end of the rack and allows for suspension movement and slight changes in steering angles.
input force
The force applied to the input piston, measured in either pounds or kilograms.
input shaft speed sensor
A sensor inside the transmission that measures the rpm of the input shaft. Also called a turbine shaft sensor.
inside micrometer
A micrometer designed to measure internal diameters.
insulator
A material that has properties that prevent the easy flow of electricity. These materials are made up of atoms with five to eight electrons in the valance ring.
insulators
A material that has properties that prevent the easy flow of electricity. These materials are made up of atoms with five to eight electrons in the valance ring.
intake air temperature (IAT) sensor
A sensor that measures the temperature of the incoming air through the air filtration system.
intake manifold vacuum
The measure of the pressure that is less than atmospheric pressure that develops in the intake manifold of a running engine equipped with a throttle plate.
intake port
The port through which the air or air/fuel mixture travels from the throttle body area to the combustion chamber.
intake stroke
The stroke of the piston from top dead center to bottom dead center during which the intake valve is open and air is pulled into the cylinder.
intake valves
Valves used in an engine to provide a means for air to enter the cylinder.
intake valve
The valve through which air and fuel enter the combustion chamber.
integral ABS systems
A brake system in which the master cylinder, power booster, and HCU are all combined in a common unit.
integral ABS system
A brake system in which the master cylinder, power booster, and HCU are all combined in a common unit.
integral valve guide
A valve guide machined into the cylinder head during cylinder head construction.
integrated circuit
A semiconductor chip that contains miniature versions of various electrical components within one housing.
integrated motor assist (IMA)
A Honda hybrid drive system that uses a moderate-sized electric motor installed between the engine and the transmission.
interference fit
A condition when two parts are held together by friction because the outside diameter of the inner component is slightly larger than the inside diameter of the outer component.
interference angle
The built-in differences in the angles between the valve seat and the valve face for the purpose of providing quick wearing-in of the surfaces; there usually must be between ½ and 1 degree of difference.
interference engine
An engine that has minimum clearance between the valves and the pistons during normal operation; in the event that the timing belt or chain breaks, the open valves will be contacted by the piston and bend the valves, possibly breaking the piston.
interlock mechanism
A mechanical device that prevents engagement of two different gears at the same time.
intermediate shaft
A steel rod positioned at an angle from the steering column to the steering gear that functions in transferring movement from one to the other.
intermediate tap
One of a series of taps designed to cut an internal thread. Also called a plug tap.
internal bleeding
The loss of blood into the body cavity from a wound; there is no obvious sign of blood.
internal combustion engine (ICE)
An engine that burns a fuel internally and creates movement due to thermal expansion of gases.
internal module control circuit
A section of the ignition module responsible for receiving the trigger signal.
internal combustion engine
An engine that burns a fuel internally and creates movement due to thermal expansion of gases.
internally equalized valve
A style of TXV where the internally equalized valve uses pressure from the inlet pipe to overcome the pressure created from the outlet pipe heat. Lower heat on the outlet pipe creates lower pressure, and the pressure from the inlet pipe is able to overcome it and move the valve.
International Standards Organization (ISO) flare
A method for joining brake lines, also called a bubble flare. Created by flaring the line slightly out and then back in, leaving the line bubbled near the end.
interrupter ring
A ferrous metal ring, shaped like a very shallow cup with slits or windows cut into it at evenly spaced intervals. The ring has the same number of blades and windows as engine cylinders and is rotated by the engine moving the blades through an air gap. The purpose of an interrupter ring is to systematically block, and expose, the magnetic field in a Hall-effect sensor in order to turn the primary ignition circuit on and off.
intrusive test
A test in which a gas analyzer hose is placed into the exhaust stream before and after the catalytic converter; it may require drilling an access hole in the exhaust pipe in front of the converter.
inverted double flare
A method for joining brake lines that forms a secure, leak-proof connection.
inverter
A device that converts direct current to alternating current.
inverters
A device that converts direct current to alternating current.
ion
An atom that has fewer electrons than protons (positive) or that has more electrons than protons (negative).
ions
An atom that has fewer electrons than protons (positive) or that has more electrons than protons (negative).
isolation valves
The valve in the hydraulic control unit that either allows or blocks brake fluid that comes from the master cylinder from entering the hydraulic control unit hydraulic circuit.
isolation valve
The valve in the hydraulic control unit that either allows or blocks brake fluid that comes from the master cylinder from entering the hydraulic control unit hydraulic circuit.
J
jack stands
Metal stands with adjustable height to hold a vehicle once it has been jacked up.
jake brake
A brake system that consists of an extra exhaust valve on a diesel engine, which releases compressed gases from the combustion chamber at the top of the compression stroke; also called a compression brake.
C
CV joint
CV is an abbreviation for constant velocity, a type of universal joint used on the drive axles or half-shafts of a vehicle. Usually refers to frontwheel drive vehicles.
CV joints
CV is an abbreviation for constant velocity, a type of universal joint used on the drive axles or half-shafts of a vehicle. Usually refers to front wheel drive vehicles.
J
journal saddles
A semicircular cut located at the bottom of the engine block that is used to support the engine crankshaft.
journal saddle
A semicircular cut located at the bottom of the engine block that is used to support the engine crankshaft.
P
PN junction
The junction between N- and P-type semiconductor materials.
K
keep alive memory (KAM)
A certain minimum amount of parasitic current draw that is used by the vehicle’s circuits to maintain memory functions and monitor systems.
keeper groove
A groove machined into the top of the valve stem near the tip of the valve that is used to “lock in” the valve keepers to help retain the valve spring onto the valve assembly.
keepers
Locking devices that keep the valve retained by the valve spring seat.
keyed lock washer
The washer that fits between the adjusting nut and the lock nut; the face of the washer is drilled with a series of holes that mate to a short pin from the adjusting nut, locking it to the spindle. Also referred to as a tang washer.
keyed washer
The washer that fits between the adjusting nut and the wheel bearing and that has the center hole keyed to fit a slot on the spindle or axle tube.
kickdown valve
A type of spool valve that is connected to the throttle on the vehicle. The valve is used to force a downshift when the throttle is opened all the way, assuming the governor pressure is below a specified point. Kickdown valves are also called detent valves.
kinetic energy
The energy of an object in motion; it increases by the square of the speed.
Kirchhoff’s current law
An electrical law stating that the sum of the current flowing into a junction is the same as the current flowing out of the junction.
knock sensor
An engine sensor that detects preignition, detonation, and knocking.
knocking
A noise heard when the air–fuel mixture spontaneously ignites before the spark plug is fired at the optimum ignition moment.
knuckle
The part that contains the wheel hub or spindle and attaches to the suspension components.
knurled
A process in which a drill bit with a spiral groove is threaded through or run through the valve guide to create raised ridges on either side of the groove, effectively shrinking the size of the valve guide.
knurling
A process in which a drill bit with a spiral groove is threaded through or run through the valve guide to create raised ridges on either side of the groove, effectively shrinking the size of the valve guide.
L
L-head
A type of four-stroke internal combustion engine having both intake and exhaust valves located in one side of the engine block, which are operated by lifters actuated by a single camshaft. It is sometimes called a flat head because there are no valves in the head.
labor guides
A guide that provides information to make estimates for repairs.
labor guide
A guide that provides information to make estimates for repairs.
lambda
The ratio of air to fuel at which all of the oxygen in the air and all of the fuel are completely burned; See also stoichiometric ratio.
latent heat of condensation
The amount of heat removal necessary to change the state from a gas to a liquid without changing the actual gauge temperature.
latent heat of evaporation
The amount of heat required to change the state from a liquid to a gas without changing the actual gauge temperature.
latent heat of freezing
The amount of heat removal required to change the state from a liquid to a solid without changing the actual gauge temperature.
lateral runout
Also called warpage, the side-to-side movement of the rotor surfaces as the rotor turns.
leading shoes
Brake shoes that are installed so that they are applied in the same direction as the forward rotation of the drum and thus are self-energizing.
leading/trailing shoe drum brake system
Type of brake shoe arrangement where one shoe is positioned in a leading manner and the other shoe in a trailing manner.
leaf springs
A spring made of one or more flat, tempered steel springs bracketed together that is used in the suspension system to support the weight of the vehicle.
leaf spring
A spring made of one or more flat, tempered steel springs bracketed together that is used in the suspension system to support the weight of the vehicle.
lemon law buyback
A consumer protection law used in some states to identify a new vehicle that has undergone several unsuccessful attempts to repair the same fault.
lever
A tool that allows the user to move a large load over a small distance at one end by applying a small force over a greater distance from the other end.
lift
The amount the valve will open. The more the valve lifts off its seat, the more air can get into and out of the engine.
lift pump
A pump that transfers fuel from the fuel tank to the fuel injection system; also called a transfer pump or supply pump.
lifter
A cylindrical component that rides on the camshaft lobe to transmit lobe movement to the valves through a linkage system.
lifters
A cylindrical component that rides on the camshaft lobe to transmit lobe movement to the valves through a linkage system.
light line technicians
A technician who diagnoses and replaces the mechanical and electrical components of motor vehicles.
light line technician
A technician who diagnoses and replaces the mechanical and electrical components of motor vehicles.
light-emitting diodes (LEDs)
A diode that emits light when current flows through it.
light-emitting diode (LED)
A diode that emits light when current flows through it.
limit switches
Switches that turn off power flow to an electric motor when a particular limit is reached.
limit value
The maximum amount of emissions that a vehicle is permitted to emit. Values are assigned to different classifications of vehicles.
limited slip differential assembly
A differential assembly that uses a clutch assembly or gear assembly to allow a limited amount of slip between the two axles. It is used to increase drive wheel traction in slippery conditions.
limited slip differentials
A differential assembly that transmits power to both wheels when one is on a slippery surface, but will still allow slippage on cornering and turns.
limp-in mode
A transmission operating mode in which limited computer controls are needed to operate for the purpose of getting the vehicle to a shop.
line bored
A process for correcting a mainline that is out of line.
line pressure
A hydraulic pressure that is used to apply bands and clutches, and is regulated by the pressure regulator valve.
line pressure sensor
A variable resistor sensor used to monitor line pressure. It sends a signal back to the PCM where it can be translated into a psi reading.
line honed
A process for correcting a mainline that is out of line.
line bored/line honed
A process for correcting a mainline that is out of line.
linear motion
Movement in a straight line.
lines
Term used interchangeably with pipes or tubes.
lip-type dynamic oil seal
A seal with a precisely shaped dynamic rubber lip that is held in contact with a moving shaft by a garter spring. An example would be a valve seal or camshaft seal.
liquefied natural gas (LNG)
A cryogenic liquid produced from gaseous methane.
liquefied petroleum gas (LPG)
Gaseous fuel at atmospheric pressure; commonly referred to as propane.
lithium soap
A thickening agent for grease to give it the proper consistency.
live axle
An axle that is powered and can move the vehicle. It is usually found on the rear of rear-wheel drive vehicles.
load transfer
Weight transfer from one set of wheels to the other set of wheels during braking, acceleration, or cornering.
lobe
The raised portion on a camshaft; used to lift the lifter and open the valve.
lobes
The raised portion on a camshaft; used to lift the lifter and open the valve.
lock cage
The stamped sheet metal cap that fits over the bearing adjustment nut and is secured by a cotter pin going through it and the spindle/axle.
lock nut
The nut that holds the adjusting nut from turning; usually tightened much tighter than the adjusting nut.
locking hub
four-wheel drive front axle hubs that are manually locked or unlocked by turning the knob on the hub.
locking pliers
A type of plier where the jaws can be set and locked into position.
locking hubs
Four-wheel drive front axle hubs that are manually locked or unlocked by turning the knob on the hub.
lockout solenoid
The cam and lock pin operated by an electronic solenoid that keeps the reverse gear in lockout until it is selected.
lockout/tagout
A safety tag system to ensure that faulty equipment or equipment in the middle of repair is not used.
long block
An engine assembly that includes the short block and adds the valve train cylinder heads, timing cover, oil pan, and, in some cases, manifolds.
longitudinal
A term used to describe the front to back engine orientation when mounted in the engine compartment.
longitudinally
The orientation of the engine in which the front of the engine is facing the front of the vehicle. It is most commonly found in rear-wheel drive vehicles.
lost foam
A metal casting process that uses a foaming process to create the pattern of the part being cast in metal.
Low Emission Vehicle (LEV) standard
A program initiated in California to improve vehicle emission standards.
low-drag calipers
A caliper designed to maintain a larger brake pad-to-rotor clearance by retracting the pistons farther than normal.
low-drag caliper
A caliper designed to maintain a larger brake pad-to-rotor clearance by retracting the pistons farther than normal.
Low-Emission Vehicle (LEV) standard
A program initiated in California to improve vehicle emission standards.
low-inductance coils
Ignition coils designed with low primary winding resistance and a low number of turns. Current flow on these coils is much higher than with contact breaker point systems and reaches its optimum level sooner.
low-pressure accumulators
A storage container for brake fluid coming from the release valves, which is under relatively low pressure.
low-pressure accumulator
A storage container for brake fluid coming from the release valves, which is under relatively low pressure.
low-pressure cycling switch
A device installed on the low-pressure line or the accumulator to turn the air-conditioning clutch on and off at specified pressures.
low-pressure switch
A device used in nonvariable air-conditioning compressors. It cycles the air conditioning clutch in response to changes in low side pressure.
low-pressure switches
A device used in nonvariable air-conditioning compressors. It cycles the air-conditioning clutch in response to changes in low side pressure.
lube technicians
A technician who carries out scheduled maintenance activities on a range of mechanical and related vehicle components.
lube technician
A technician who carries out scheduled maintenance activities on a range of mechanical and related vehicle components.
lubricating oil
Processed crude oil with additives to help it perform well in the engine.
lubrication system
A system of parts that work together to deliver lubricating oil to the various moving parts of the engine.
lubricity
The ability to lubricate moving parts.
lug
A flange that is shaped to assist with aligning objects on other objects.
lug nuts
Nuts that secure the wheel onto the wheel studs.
lug wrench
A tool designed to remove wheel lugs nuts that is commonly shaped like a cross.
lugs
A flange that is shaped to assist with aligning objects on other objects.
M
M85 vehicles
A flexible-fuel vehicle, meaning any mixture of methanol and gasoline/petrol in the fuel tank can be used by the engine.
M85 vehicle
A flexible-fuel vehicle, meaning any mixture of methanol and gasoline/petrol in the fuel tank can be used by the engine.
MacPherson strut
A strut used on an independent suspension where the spring and shock are joined together. Used on most front-wheel drive vehicles.
magnafluxed
An electromagnetic process used to locate cracks in ferrous engine blocks and cylinder heads and other ferrous metal parts.
magnafluxing
An electromagnetic process used to locate cracks in ferrous engine blocks and cylinder heads and other ferrous metal parts.
magnetic pickup tools
An extending shaft, often flexible, with a magnet fitted to the end for picking up metal objects.
magnetism
The force that attracts or repels magnetic charges; or the property of a material to respond to a magnetic field.
magneto-resistive
A type of wheel speed sensor that uses an effect similar to a Hall effect sensor to create its signal.
magneto-resistive sensor
A type of wheel speed sensor that uses an effect similar to a Hall effect sensor to create its signal.
magneto-rheological fluid
A fluid that has the unique characteristic of changing viscosity when exposed to a magnetic field.
main bearings
A bearing that supports the crankshaft in the block and provides a lubrication surface for the main journals.
main bearing caps
Sturdy caps placed over the main journals of the crankshaft assembly and fastened with either two or four bolts.
main bearing journals
A bearing surface that supports the crankshaft in the engine block.
main cap girdle
A metal attachment that strengthens and connects all the main bearing caps together. It can be integral from the main bearing caps, or separate.
main journals
The smooth machined area of the crankshaft assembly that allows the crankshaft to rotate within the main bearings.
main bearing journal
A bearing surface that supports the crankshaft in the engine block.
main bearing
A bearing that supports the crankshaft in the block and provides a lubrication surface for the main journals.
main journal
The smooth machined area of the crankshaft assembly that allows the crankshaft to rotate within the main bearings.
mainline
The imaginary centerline down the engine cylinder block.
mains
The specific round smooth journals of the crankshaft that rotate in main bearings.
male and female terminals
A crimp or solder terminal on which the male and female ends join to create a removable low-resistance connection.
male and female terminal
A crimp or solder terminal on which the male and female ends join to create a removable low-resistance connection.
Malfunction indicator light (MIL)
An indicator located in the instrument cluster that illuminates when the power train control module (PCM) detects a fault in one of the vehicle systems. Formerly called a check engine or service engine soon light.
malfunction indicator lamp (MIL)
An indicator located in the instrument cluster that illuminates when the power train control module (PCM) detects a fault in one of the vehicle systems. Formerly called a check engine or service engine soon light.
Mallory metal
A tungsten alloy of copper and nickel that is used as a metal substitute added to the crankshaft counterweight for balancing purposes.
mandrel
The shaft of a pop rivet.
mandrel forming
The special bending of pipe to ensure the pipe does not collapse. The use of a pipe bender with mandrels allows for very tight bends without creating kinks or reducing the size of the pipe.
mandrel head
The head of the pop rivet that connects to the shaft and causes the rivet body to flare.
manifold absolute pressure (MAP) sensor
A vacuum sensor that is attached to the intake manifold by a passageway or vacuum hose. The sensor measures engine intake manifold pressure to determine engine load and sends a corresponding signal to the PCM.
manual bleeding
A bleeding method where one person manually operates the brake pedal while the other person opens and closes the bleeder screws on the wheel brake units to allow the air and old brake fluid to be pushed out.
manual adjustable-rate shock absorber
A shock absorber that allows manual adjustment of the dampening rate.
manual climate control system
A climate control system fully controlled by the operator.
manual lever position (MLP) switch
A switch that is used by the PCM to tell which gear range the driver has selected with the shift lever.
manual
A climate control system fully controlled by the operator.
manually adjustable air spring
A rubber air bag placed inside coil springs to increase the spring’s load-carrying ability. It is filled manually through a valve similar to a tire valve stem.
manually adjustable-air spring
A rubber air bag placed inside coil springs to increase the spring’s load-carrying ability. It is filled manually through a valve similar to a tire valve stem.
mass airflow (MAF) sensor
A sensor located in the air intake system that is used to measure the mass of the air flowing into the engine.
mass airflow sensor
CM input that measures the mass of the air entering the engine.
master cylinder
Converts the brake pedal force into hydraulic pressure, which is then transmitted via brake lines and hoses to one or more pistons at each wheel brake unit.
match mounting
The process of matching up the tire’s highest point with the rim’s lowest point for the purpose of reducing the tire’s radial runout.
material safety data sheets (MSDS)
A sheet that provides information about handling, use, and storage of a material that may be hazardous.
material safety data sheet (MSDS)
A sheet that provides information about handling, use, and storage of a material that may be hazardous.
measuring tapes
A thin measuring blade that rolls up and is contained in a spring-loaded dispenser.
measuring tape
A thin measuring blade that rolls up and is contained in a spring-loaded dispenser.
mechanical advantage
The process of using a device to get more output force than the amount of input force, with the trade-off being that the input distance is proportionately longer than the output distance.
mechanical disadvantage
When the load distance on a lever is greater than the effort distance, which means the effort required to move the load is greater than the load itself.
mechanical fingers
Spring-loaded fingers at the end of a flexible shaft that pick up items in tight spaces.
mechanical jacks
A type of vehicle jack that uses mechanical leverage to lift a vehicle.
mechanical pressure control regulator valve
A spool valve and spring assembly that are used to control the amount of line pressure in a transmission.
mechanical jack
A type of vehicle jack that uses mechanical leverage to lift a vehicle.
membrane electrode assembly
The individual voltage-producing component in a fuel cell stack.
memory saver (memory minder)
Battery backup device for vehicle computer systems.
mercaptan
An agent that smells like sulfur that is added to liquefied petroleum or natural gas to aid in detecting leaks.
meshed pinion
A pinion when it is mated with the rack.
metallurgical bonding
A process of sintering metals until they are fused together as one metal.
metallurgically bonded
A process of sintering metals until they are fused together as one metal.
metering valves
A valve used on vehicles equipped with older rear drum/front disc brakes to delay application of the front disc brakes until the rear drum brakes are applied. Located in line with the front disc brakes.
metering jet
A calibrated orifice in a carburetor for fuel to flow through. Often it is replaceable for performance or economy desires.
metering valve
A valve used on vehicles equipped with older rear drum/front disc brakes to delay application of the front disc brakes until the rear drum brakes are applied. Located in line with the front disc brakes.
methanol
A motor fuel made from wood alcohol.
microleak detector
A solution used to detect refrigeration leaks.
micrometer
An accurate measuring device for internal and external dimensions. Commonly abbreviated mic.
micrometers
An accurate measuring device for internal and external dimensions. Commonly abbreviated mic.
micron
A unit of measurement equal to 0.000039” (0.001 mm).
micron gauge
A device designed to measure vacuum very precisely.
microprocessor
An electronic control unit that can process data and control one or more devices.
microprocessors
An electronic control unit that can process data and control one or more devices.
Miller cycle
An engine cycle that uses a longer effective power stroke than intake stroke through delayed closing of the intake valve. This engine uses a supercharger to pressurize air into the cylinder when needed.
min/max setting
A setting on a DVOM to display the maximum and minimum readings.
mineral oil
Base stock processed from crude oil in a refinery, used as the base material of all conventional oil.
minivan
A lighter-duty van used for carrying six to eight occupants or light cargo.
minivans
A lighter-duty van used for carrying six to eight occupants or light cargo.
misfire
Failure of one or more cylinders to fire or complete combustion.
modulator pressure
A pressure created by the vacuum modulator that is proportional to engine load. Modulator pressure is used to delay transmission upshifting based upon engine load. It may also be used to raise line pressure to more firmly apply bands and clutches under higher engine loads.
module
An electronic computer or circuit board that controls specific functions.
modules
An electronic computer or circuit board that controls specific functions.
moly
The abbreviation for the lubricant called molybdenum disulfide.
molybdenum thickening agents
A compound used in some greases to give it the needed consistency.
molybdenum thickening agent
A compound used in some greases to give it the needed consistency.
monitor
An OBDII test run to ensure that a specific component or system is working properly.
monitors
An OBDII test run to ensure that a specific component or system is working properly.
morse taper
A tapered mounting shaft for drill bits and chucks in larger drills and lathes.
morse-style chain
A heavy-duty chain constructed of many links and held together with pins. It is used in some transaxles and transfer cases to transmit torque from one component to another.
muffler
A device to quiet the pipes of the air-conditioning system with baffles placed inside to deaden the sound of refrigerant moving.
mufflers
A device to quiet the pipes of the airconditioning system with baffles placed inside to deaden the sound of refrigerant moving.
multidisc clutches
A type of holding device used by an automatic transmission to stop the movement of one component of a planetary gear set. It uses several thin friction discs and thin steel plates that are squeezed together when hydraulic pressure is applied to a piston in the clutch.
multidisc clutch
A type of holding device used by an automatic transmission to stop the movement of one component of a planetary gear set. It uses several thin friction discs and thin steel plates that are squeezed together when hydraulic pressure is applied to a piston in the clutch.
multilayer steel (MLS) head gasket
A gasket composed of multiple layers of steel and coated with a rubberlike substance that adheres to metal surfaces. They are typically used between the cylinder head and the cylinder block.
multimeter
A test instrument used to measure volts, ohms, and amps. A digital multimeter may also be called a digital volt-ohmmeter (DVOM).
multiphase
An electric motor that operates through more than one phase.
multiplate clutch
A clutch assembly that is comprised of two or more clutch plates and used to increase the torque-carrying capacity of the clutch.
multiplex
The carrying of multiple signals on one wiring circuit. Digital signals are multiplexed on a dedicated CAN-bus or similar network. Also referred to by the abbreviation MUX.
multiplexed
The carrying of multiple signals on one wiring circuit. Digital signals are multiplexed on a dedicated CAN-bus or similar network. Also referred to by the abbreviation MUX.
multipoint fuel injection (MPFI)
An injection system in which fuel is injected into the intake ports just upstream of each cylinder’s intake valve, rather than at a central point within an intake manifold. Also called multiport injection.
mylar tape
Polyester film that may be metalized and incorporated into a wiring harness to provide electrical shielding.
N
N-type
Semiconductor material with a small amount of extra electrons.
National Lubricating Grease Institute (NLGI)
An organization that grades the thickness of automotive and industrial grease.
National Automotive Technicians Education Foundation (NATEF)
An accrediting body for secondary and post-secondary automotive training programs; an independent, nonprofit organization under the umbrella of the ASE.
National Fire Protection Association (NFPA)
The agency that publishes standards for liquefied petroleum and compressed natural gas vehicles.
natural gas
Methane; often referred to simply as NG.
needle roller bearings
Typically a small-diameter pin rolling bearing that can be held in a cage or placed into the inside diameter of a hole.
needle roller bearing
Typically a small-diameter pin rolling bearing that can be held in a cage or placed into the inside diameter of a hole.
needle-nosed pliers
Pliers with long tapered jaws for gripping small items and getting into tight spaces.
negative back pressure EGR valve
A dual-diaphragm EGR valve that uses vacuum in the exhaust manifold to operate a control diaphragm that opens and closes a vent in the main diaphragm chamber.
negative camber
Tilt of the top of the tire toward the centerline of the vehicle.
negative caster
Forward tilt of the wheel pivot points from the vertical line.
negative offset
A condition in which the plane of the hub mounting surface is positioned toward the brake side or back of the wheel centerline.
negative scrub radius
A condition in which the point of center contact between the road surface and the tire and the point where the steering axis centerline contacts the road surface intersect above the road surface.
negative temperature coefficient (NTC)
A characteristic of materials whereby resistance decreases as temperature increases.
negative temperature coefficient (NTC) thermistor
A thermistor that gains resistance as temperature goes down and loses resistance as temperature goes up.
neutral steer
A condition in which both the front and the rear tires of a vehicle are experiencing the same slip angle.
Newton’s first law of motion
A physical law that states that “an object will stay at rest or uniform speed unless it is acted upon by an outside force.”
NFPA-52
A document from the NFPA that sets standards for compressed natural gas refueling stations and compressed natural gas vehicle fuel systems.
nippers (pincer pliers)
Pliers designed to cut protruding items level with the surface.
nippers
Pliers designed to cut protruding items level with the surface.
nitriding
A metal surfacing process that uses nitrogen ammonia gas to create a very thin, highly hardened surface.
nitridization process
The nitriding metal surfacing process in which nitrogen ammonia gas is used inside a furnace and heated up and then cooled.
nitrile butadiene rubber (NBR)
A man-made rubber that is more resistant to oils and acids than natural rubber; it is compatible with R-12.
nitrogen oxides (NO ₂ )
The various compounds of nitrogen that contributed to a smog-forming pollutant emitted from the tailpipe.
nitrogen oxides
The various compounds of nitrogen that contributed to a smog-forming pollutant emitted from the tailpipe.
nitrogen oxides (NOₓ)
The various compounds of nitrogen that contributed to a smog-forming pollutant emitted from the tailpipe.
noise, vibration, and harshness (NVH) test
A test to measure for any audible noises, vibrations, and harsh operation. It can be completed by the technician with or without the aid of an NVH tester. The tester is used to pinpoint the exact frequencies of the noise and vibrations.
non-directional tread patterns
A tread pattern that is nonspecific, allowing the tire to be placed on any wheel of a vehicle.
non-integral valve guide
Also called a replaceable valve guide, a valve guide that is pressed into the cylinder head after the head has been constructed. These guides can be removed and replaced.
noncontinuous monitor
A monitor that runs only once per drive cycle.
nondirectional tread pattern
A tread pattern that is nonspecific, allowing the tire to be placed on any wheel of a vehicle.
nonintegral ABS systems
A brake system in which the master cylinder, power booster, and HCU are all separate units.
normally closed (NC)
An electrical contact that is closed in the at-rest position.
normally open (NO)
An electrical contact that is open in the at-rest position.
NPN transistor
A transistor in which P-type material is sandwiched between two layers of N-type material.
number one cylinder
Typically the cylinder located farthest forward on the engine. It is the first cylinder in the firing order.
nut
A fastener with a hexagonal head and internal threads for screwing on bolts.
nuts
A fastener with a hexagonal head and internal threads for screwing on bolts.
O
O-ring seals
A seal that is a complete circle. If a cutaway is done, it will also be a complete circle. These seals are usually set into a groove that is machined into the housing or part that does not move and is intended to be sealed.
O-ring valve stem seals
A seal used where the valve spring retainer attaches to the valve stem to seal the juncture and prevent excessive oil from leaking into the valve stem.
O-ring seal
A seal that is a complete circle. If a cutaway is done, it will also be a complete circle. These seals are usually set into a groove that is machined into the housing or part that does not move and is intended to be sealed.
O-ring valve stem seal
A seal used where the valve spring retainer attaches to the valve stem to seal the juncture and prevent excessive oil from leaking into the valve stem.
O-ring
Rubber-type rings available in different sizes used to seal pipe fittings.
O-rings
A small donut shaped rubber ring used to seal connections between air-conditioning components.
OBDI
The first generation of on-board diagnostic systems that originated for California vehicles.
OBDII
The second generation of on-board diagnostic systems, which have been in effect for all US vehicles since 1996.
Occupational Safety and Health Administration (OSHA)
Government agency created to provide national leadership in occupational safety and health.
octane rating
A standard measure of the performance of a motor or aviation fuel. The higher the octane number, the more heat the fuel can withstand before self-igniting.
odorant
An agent (mercaptan) that smells like sulfur that is added to liquefied petroleum or natural gas to aid in detecting leaks.
off-car brake lathe
A tool used to machine (refinish) drums and rotors after they have been removed from the vehicle.
offset area
An area on the crankshaft that is offset from the crankshaft centerline and that becomes a counterweight.
offset screwdriver
A screwdriver with a 90-degree bend in the shaft for working in tight spaces.
offset vice
A vice that allows long objects to be gripped vertically.
ohm
The unit for measuring electrical resistance.
ohms
The unit for measuring electrical resistance.
Ohm’s law
A law that defines the relationship between current, resistance, and voltage.
oil control rings
The widest of the metal rings on the piston head assembly that controls oil flow to and from the cylinder walls.
oil cooler
A device that takes heat away from engine oil by passing it near either engine coolant or outside air. Cooling the engine oil helps to keep it from overheating and breaking down.
oil filter wrench
A specialized wrench that allows extra leverage to remove an oil filter when it is tight.
oil monitoring systems
A system that alerts the driver when it is time to change engine oil. These systems will need to be reset for the customer after an oil change is performed.
oil pan
The metal pan that covers the bottom of the engine, contains oil sump where engine oil is held.
oil pressure relief valve
A valve usually located in the oil pump that limits the oil pressure. When oil pressure is reached, excessive pressure is bled back to the sump.
oil pump
A device that pumps lubricating oil through the engine.
oil pump strainer
A screen located on the oil pump pickup that keeps debris from being picked up by the oil pump.
oil ring groove
A metal groove cut into the piston head assembly designed to hold the oil control ring, which lubricates the cylinder wall and pistons.
oil seals
Any seal used to seal oil in and dirt, moisture, and debris out.
oil slinger
A device that rides partially in the transmission fluid; as it spins, it flings oil to lubricate the internal workings of the transmission.
oil spurt holes
Holes drilled into the connecting rod that spray oil up onto the cylinder walls and the piston wrist pins.
oil sump
The lower part of the oil pan that holds lubricating oil for the engine. The oil pickup screen sits in this low point.
oil galleries
Oil passages that are drilled into the engine block and cylinder head(s). These passageways carry oil from the oil pump to critical moving parts.
oil control ring
The widest of the metal rings on the piston head assembly that controls oil flow to and from the cylinder walls.
oil monitoring system
A system that alerts the driver when it is time to change engine oil. These systems will need to be reset for the customer after an oil change is performed.
oil seal
Any seal used to seal oil in and dirt, moisture, and debris out.
oiler
A device used to add oil to the air-conditioning system.
on-board diagnostic (OBD)
The first generation of a self-diagnostic system built into the vehicle computer system that provided a means of warning the driver when the computer detected a problem in the system. This system allowed the technician to retrieve codes to assist in diagnosis of the vehicle.
on-board diagnostics II (OBDII)
This generation of self-diagnostic systems mandated standardized diagnostic trouble codes and a data link connector. It also mandated monitoring of certain emission systems, such as the catalytic converter, oxygen sensor, EGR, and evaporative emissions.
on-board diagnostic (OBDI)
The first generation of a self-diagnostic system built into the vehicle computer system that provided a means of warning the driver when the computer detected a problem in the system. This system allowed the technician to retrieve codes to assist in diagnosis of the vehicle.
on-board diagnostic II (OBDII)
This generation of self-diagnostic systems mandated standardized diagnostic trouble codes and a data link connector. It also mandated monitoring of certain emission systems, such as the catalytic converter, oxygen sensor, EGR, and evaporative emissions.
on-car brake lathe
A tool used to machine (refinish) rotors while they are still attached to the vehicle.
on/off–type signal
A signal that is either a 12-volt signal or zero volts. Typically, switches provide on/off signals. Some systems use a 5-volt reference signal instead of a 12-volt signal.
one-way clutches
A type of holding device used by an automatic transmission to stop the movement of one component of a planetary gear set. It allows free spinning in one direction but will lock up when the part attempts to spin in the opposite direction.
one-way clutch
A type of holding device used by an automatic transmission to stop the movement of one component of a planetary gear set. It allows free spinning in one direction but will lock up when the part attempts to spin in the opposite direction.
open circuit
A circuit that has a break that prevents current from flowing.
open
A term used to describe a circuit that does not have a complete path for current to flow.
open differential assembly
A differential assembly that allows both axles to turn at their own speed when turning a corner, but is dependent on the traction of the tires to deliver torque to the ground. If one wheel has no traction, all of the engine’s torque will be used at that wheel, causing it to simply spin.
open fracture
A fracture in which the bone is protruding through the skin or there is severe bleeding.
open-end wrench
A wrench with open jaws to allow side entry to a nut or bolt.
optical cables
A cable that contains a number of optical fibers.
optical sensor
A sensor that generates a voltage when excited by a beam of light.
optical cable
A cable that contains a number of optical fibers.
orifice
A precisely sized hole used to reduce the speed and pressure of hydraulic oil flowing to a clutch or band.
orifices
A precisely sized hole used to reduce the speed and pressure of hydraulic oil flowing to a clutch or band.
oscillate
To cycle above and below a given value.
oscillation
The fluctuation of an object between two states. With regard to suspension springs, it refers to the uncontrolled compression and decompression of the spring following overshoot.
oscillations
The fluctuation of an object between two states. With regard to suspension springs, it refers to the uncontrolled compression and decompression of the spring following overshoot.
oscilloscope
A tool that shows graphically what is happening to voltage over a period of time; it is used to diagnose electrical faults.
oscilloscopes
A tool that shows graphically what is happening to voltage over a period of time; it is used to diagnose electrical faults.
outer race
The outside component of a wheel bearing that has a smooth, hardened surface for rollers or balls to ride on.
outer tie-rod
The tie-rod attached between the tie-rod and the steering arm. It transfers the movement of the rack, pivoting as the rack is extended or retracted when the vehicle is negotiating turns.
outlet port
Links the cylinder to the brake lines.
output force
Force that equals the working pressure multiplied by the surface area of the output piston, expressed as pounds, newtons, or kilograms.
output signals
The voltage sent to solenoids and motors by the PCM to do work.
output signal
The voltage sent to solenoids and motors by the PCM to do work.
outside micrometer
A precision measuring instrument meant to measure the outside of components. It is usually accurate to 0.0001" (0.0025 mm).
overcharging
Overfilling of the air-conditioning system; may result in poor cooling or mechanical failure of the system.
overdrive
Any gear ratio that results in a torque reduction with a speed increase. Overdrive is used on vehicles to reduce the engine speed when traveling at highway speed in order to save fuel.
overflow tank
A tank used to catch any coolant that is released from the radiator cap (works like a catch can).
overhauling
The process of refurbishing the transmission to like-new condition.
overhead cam (OHC) engine
An I-head engine with the camshaft located on top of the cylinder head rather than in the block.
overhead valve (OHV) engine
An engine in which the valves are positioned in the cylinder head assembly, directly over the top of the piston
overhead cam (OHC)
An I-head engine with the camshaft located on top of the cylinder head rather than in the block.
overshoot
The amount a spring extends (springs back) past its original length following compression.
oversteer
A condition in which a vehicle’s front slip angles are larger than the rear slip angles. This vehicle is said to be “pushing” in the corners.
owner’s manual
An informational guide supplied by the manufacturer; it contains basic vehicle operating information.
oxidation inhibitors
An oil additive that helps keep hot oil from combining with oxygen to produce sludge or tar.
oxidation inhibitor
An oil additive that helps keep hot oil from combining with oxygen to produce sludge or tar.
oxides of nitrogen
A vehicle emission that contributes to ground-level ozone. Oxides of nitrogen are produced when nitrogen and oxygen react during combustion, given sufficient temperatures and pressures. Forms include nitrogen oxide and nitrogen dioxide.
oxyacetylene torches
A gas welding system that combines oxygen and acetylene.
oxyacetylene torch
A gas welding system that combines oxygen and acetylene
oxygen sensor (before and after catalytic converter)
An exhaust sensor used to measure the amount of oxygen in the exhaust gases produced by the engine PCM, used to determine fuel mixture and spark timing.
P
P-type
Semiconductor material with holes where electrons are missing.
paddle
A shifting mechanism or electronic control usually attached to the steering wheel.
paddles
A shifting mechanism or electronic control usually attached to the steering wheel.
pan inspection
The process of removing the transmission pan to check for clutch material, metal, and other debris or contaminants.
panhard rod
A metal rod used to hold the dead axle and keep it from moving from side to side through corners. It is mounted on the body or frame of the vehicle and the axle. Also referred to as a track bar.
parade pattern
The display of all the cylinders firing in sequence on an oscilloscope.
parallax error
A visual error caused by viewing measurement markers at an incorrect angle.
parallel flow condensers
A condenser with multiple parallel tubes flowing from one side tank to the other.
parallel hybrid
A hybrid vehicle driven simultaneously by an internal combustion engine and an electric machine.
parallel hybrid drive train
A type of hybrid transmission in which power can flow from either a gasoline engine or an electric motor and any combination of the two.
parallel flow condenser
A condenser with multiple parallel tubes flowing from one side tank to the other.
parallelism
Also called thickness variation; both surfaces of the rotor should be perfectly parallel to each other so that brake pulsations do not occur.
parallelogram steering system
A non–rack-and-pinion system that uses a series of parts consisting of the pitman arm, idler arm, center link, and tie-rod assemblies that relays movement from the steering gearbox to the wheel assembly.
parasitic draw
Unwanted drain on the vehicle battery when the vehicle is off.
parasitic losses
A loss of engine efficiency caused by internal friction, inefficient breathing, etc.
parasitic loss
A loss of engine efficiency caused by internal friction, inefficient breathing, etc.
parking brake cable removal tool
A tool used to compress the spring steel fingers of the parking brake cable so that the cable can be removed from the backing plate.
parking brake mechanism
A mechanism that operates the brake shoes or pads to hold the vehicle stationary when the parking brake is applied.
parking brake
A brake system used for holding the vehicle when it is stationary.
parking brake cables
A mechanism used to transmit force from the parking brake actuating lever to the brake unit.
parking brake cable pliers
A tool used to install parking brake cables.
parking brake cable
A mechanism used to transmit force from the parking brake actuating lever to the brake unit.
particulate matter (PM)
Unseen microscopic particles of carbon consisting of soot (especially prominent with diesel exhaust). PM clogs the lungs and is carcinogenic.
particulate matter
Unseen microscopic particles of carbon consisting of soot (especially prominent with diesel exhaust). PM clogs the lungs and is carcinogenic.
parts programs
A computer software program for identifying and ordering replacement vehicle parts.
parts specialists
The person who serves customers at the parts counters.
parts program
A computer software program for identifying and ordering replacement vehicle parts.
parts specialist
The person who serves customers at the parts counters.
Pascal’s law
The law of physics that states that pressure applied to a fluid in one part of a closed system will be transmitted equally to all other areas of the system.
passive keyless entry (PKE)
An active system that senses the proximity of a fob and locks or unlocks the vehicle.
PCV valve
A valve that controls the amount of crankcase ventilation flow that is allowed and varies with changes in manifold pressure.
peening
A term used to describe the action of flattening a rivet through a hammering action.
performance testing
The process of recreating a driving situation to check air-conditioning performance and vent temperature.
permanent magnet electric motor
An electric motor in which the magnetic field in the casing is produced by permanent magnets, while the armature has an electromagnetic field generated by passing electrical current through loops or windings, thereby producing the motor action.
permanent magnet
A material with natural or man-made constant magnetic properties.
permanently mounted tanks
A compressed natural gas or propane cylinder not designed to be portable.
permanently mounted tank
A compressed natural gas or propane cylinder not designed to be portable.
personal protective equipment (PPE)
Safety equipment designed to protect the technician, such as safety boots, gloves, clothing, protective eyewear, and hearing protection.
phase
A term used to describe one set of windings from an alternator or alternating current electric motor.
phaser
A device that is able to shift camshaft timing while the camshaft is turning. This device takes the place of the standard timing belt pulley or timing chain gear.
phenolic resin
A material used to create some brake pistons that is very resistant to corrosion and heat transfer.
Phillips head screwdriver
A type of screwdriver that fits a head shaped like a cross in screws.
photochemical smog
A brown haze that hangs in the sky, typically seen over large cities. Smog is a major health issue to humans because it affects lung tissue.
photodiode
An electronic component that creates a varying voltage or current output based on the amount of light striking it.
photovoltaic (PV) effect
The conversion of sunlight into electricity.
pick-up assembly
A component with a wire coil wrapped around a ferrous metal core; it is used to generate an electrical signal when a magnetic field passes through it.
pick-up
A vehicle that carries cargo; it has stronger chassis components and suspension than a sedan.
pickup tube
A tube connected to the oil pump that acts like a straw for the oil pump to pull oil from the sump of the oil pan.
piezoelectric
A type of electricity in which a material such as a quartz crystal produces voltage when mechanical pressure distorts it.
pilot bearing
The bearing or bushing that supports the front of the transmission input shaft.
pin punches
A type of punch in various sizes with a straight or parallel shaft.
pin punch
A type of punch in various sizes with a straight or parallel shaft.
pinging
A preignition or detonation concern that is damaging to the engine if it is allowed to continue. It is described as the sound of marbles being shaken in a glass jar.
pinion shaft
On a drive axle using a ring-and-pinion gear assembly, the input component that drives the ring gear.
pinion
A gear located at the end of the steering shaft connected to the rack. It moves the rack from side to side as the pinion rotates, controlling the direction of the wheels.
pinions
The small gears in a planetary gear set that revolve around the sun gear, also known as planetary gears.
pintle
A tapered valve that sits in a tapered seat to seal a passageway for air or fuel.
pip marks
A small indent or dimple on the piston ring that indicates which side of the ring is installed upward. It is also used on some timing sprockets.
pip mark
A small indent or dimple on the piston ring that indicates which side of the ring is installed upward. It is also used on some timing sprockets.
pipe wrench
A wrench that grips pipes and can exert a lot of force to turn them. Because the handle pivots slightly, the more pressure put on the handle to turn the wrench, the more the grip tightens.
piston
The round metal plug found inside the engine cylinder that moves up and down inside the cylinder.
piston assembly
All of the parts of the piston including the piston, piston rings, and piston pin.
piston clearance
The clearance between the piston and the cylinder wall that allows for lubricating oil to reduce friction.
piston displacement
The volume of air that is moved by the piston from bottom dead center to top dead center.
piston engine
An internal combustion engine that uses cylindrical pistons moving back and forth in a cylinder to extract mechanical energy from chemical energy.
piston pin (wrist pin)
A round circular metal manufactured part that attaches the piston assembly to the connecting rod assembly.
piston pin boss
The reinforced area of the piston where the piston wrist pin attaches the piston to the connecting rod.
piston rings
A metal ring that is placed in a square groove around a piston for sealing purposes.
piston ring grooves
A square-cut groove located on the piston designed to hold a metal piston ring.
piston skirt
The area below the ring groove area of the piston that prevents the piston from cocking and becoming jammed in the cylinder bore.
piston slap
An engine noise caused by excessive clearance between the piston skirt area and the cylinder wall.
piston stroke
The distance the piston travels through the engine cylinder from top dead center to bottom dead center.
piston ring groove
A square-cut groove located on the piston designed to hold a metal piston ring.
piston ring
A metal ring that is placed in a square groove around a piston for sealing purposes.
pitch circle diameter (PCD)
The diameter of the imaginary circle drawn through the center of the wheel bolt holes.
pitch
The angle of a fan blade. A steeper pitch draws more air, while a shallower pitch draws less air.
pitch (bolts)
On a helix, the distance moved in one full revolution of the cylinder.
pitch (brakes)
Movement of a vehicle around its y-axis (the imaginary line across the center of the vehicle from left to right) that causes the vehicle to lower or rise on the front end during quick braking or acceleration.
planet carrier
The device that holds the planet gears in place, keeping them equally spaced.
planetary gears
The small gears in a planetary gear set that revolve around the sun gear; also known as pinion gears.
plasma cutter
A tool that uses electricity and compressed gas to produce a stream of high-temperature gas to cut metal.
Plastigauge®
The trademarked name for a plastic gauging material used to check the clearances between two surfaces.
plate
A flat thin square or rectangular sheet of material often used to describe the arrangement of positive and negative electrodes in batteries.
plates
A flat thin square or rectangular sheet of material often used to describe the arrangement of positive and negative electrodes in batteries.
plenum chamber
A large portion of the intake manifold after the throttle plate and before the intake runner tubes. The plenum provides a reservoir of air and helps prevent interference with the flow of air between individual branches.
pliers
A hand tool with gripping jaws.
plug-in hybrid electric vehicle (PHEV)
A hybrid electric vehicle in which only one power source, the battery, is used to propel the vehicle for a certain distance, limited by the storage capacity of the battery and the efficiency of the motor.
plunge-type joint
The inner joint on the half shaft that allows for changes in shaft length.
ply rating
A rating system that denotes the number of belt layers or plies that make up the tire carcass. In radial tires, ply rating denotes the relative strength of the plies, not the actual number of plies.
pneumatic jacks
A type of vehicle jack that uses compressed gas or air to lift a vehicle.
pneumatic jack
A type of vehicle jack that uses compressed gas or air to lift a vehicle.
PNP transistor
A transistor in which N-type material is sandwiched between two layers of P-type material. This type of semiconductor material has holes, meaning it is missing electrons.
pocket bearings
A roller in the rear of the input shaft that supports the front of the main shaft.
pocket bearing
A roller in the rear of the input shaft that supports the front of the main shaft.
polarity
The state of charge, positive or negative.
polarity sensitive
A term used to describe a component that must be connected into a circuit with the correct polarity to its terminals.
policy
A guiding principle that sets the shop direction.
pollutant
A potential threat to human health or the environment resulting from excessive amounts of chemicals and waste.
pollutants
A potential threat to human health or the environment resulting from excessive amounts of chemicals and waste.
polyalphaolefin (PAO)
A man-made base stock (synthetic) used in place of mineral oil. Oil molecules are more consistent in size and no impurities are found in this oil since it is made in a lab.
polycrystalline diamond (PCD) cutter
An engine block resurfacing tool used on aluminum parts.
pop rivet guns
A hand tool for installing pop rivets.
pop rivet gun
A hand tool for installing pop rivets.
poppet valve
A valve that controls the flow of brake fluid at usually preset pressures.
poppet (mushroom) valve
A cam-operated, spring-loaded mushroom-type valve used to control intake into, and exhaust out of, the combustion chamber.
poppet, or mushroom, valve
A cam-operated, spring-loaded mushroom-type valve used to control intake into, and exhaust out of, the combustion chamber.
portable universal cylinders
A liquefied petroleum gas tank that can be moved or transported.
portable universal cylinder
A liquefied petroleum gas tank that can be moved or transported.
positive back pressure EGR valve
A dual-diaphragm EGR valve that uses pressure in the exhaust system to act on the control diaphragm, which closes a bleed valve in the main diaphragm, allowing the EGR valve to open only when there is positive exhaust pressure.
positive camber
Tilt of the top of the tire out from the centerline of the vehicle.
positive caster
Backward tilt of the wheel pivot points from the vertical line.
positive crankcase ventilation (PCV) system
A system that draws blow-by gases from the crankcase into the intake to be burned.
positive offset
A condition in which the plane of the hub mounting surface is positioned toward the outside or front of the wheel centerline.
positive scrub radius
A condition in which the point of center contact between the road surface and the tire and the point where the steering axis centerline contacts the road surface intersect below the road surface.
positive temperature coefficient (PTC)
A characteristic of materials whereby resistance increases as temperature increases.
positive valve stem seals
A valve seal located at the top of the valve guide that is a more positive seal than an umbrella or O-ring seal.
positive crankcase ventilation (PCV)
A system that draws blow-by gases from the crankcase into the intake to be burned.
positive valve stem seal
A valve seal located at the top of the valve guide that is a more positive seal than an umbrella or O-ring seal.
potentiometer
A sensor that acts as a variable resistor when a wiper arm moves across its resistive material.
potentiometers
A variable resistor that can be used to adjust voltage in a circuit.
pour point
The temperature below which the fuel will not flow.
pour point depressants
Oil additives that keep wax crystals from forming and causing the oil to gel during cold operation.
powdered metal rod
A connecting rod manufactured through the process of heat, compression, and forging of powdered metals into a connecting rod.
power
The rate at which work is done; electrical power is measured in watts.
power windings
The current-carrying winding in an alternator or motor.
power assist unit
The electric motor in electric power assist steering systems.
power chips
An aftermarket performance programmable chip marketed to increase horsepower and mileage of electronically controlled diesel engines.
power divider/splitter
A device that receives power from an internal combustion engine and electric machine to power a hybrid electric vehicle.
power flow
The path that power takes from the beginning of an assembly to the end. In a transmission, power flow changes as different gears are selected by the driver.
power section
A chamber in the rack where pressurized fluid acts upon pistons that assist in steering.
power steering
An option on a vehicle that allows movement of the steering wheel with decreased driver effort.
power steering pump
A small hydraulic pump that provides assistance to the driver when turning the steering wheel.
power stroke
The stroke in an engine cycle after ignition, when the piston again moves from top to bottom under the power.
power take-off (PTO)
A device attached to the transmission that is gear driven and can be used to run accessories such as winches and towing equipment. It can also refer to the gears that send power to the rear axle in a predominantly front wheel drive vehicle.
power tools
Tools powered by electricity or compressed air.
power train control module (PCM)
A computer or electronic control unit that controls engine and related vehicle systems.
power train mount
A rubber or metal bracket used to secure the engine and transmission into the vehicle. Some vehicles use hydraulic or electrohydraulic power train mounts.
power unit
A belt- or gear-driven pump that produces hydraulic pressure for use in the steering box or rack.
power chip
An aftermarket performance programmable chip marketed to increase horsepower and mileage of electronically controlled diesel engines.
power winding
The current-carrying winding in an alternator or motor.
power train mounts
A rubber or metal bracket used to secure the engine and transmission into the vehicle. Some vehicles use hydraulic or electrohydraulic power train mounts.
power-on-demand
A feature that shuts down the engine when not needed to save fuel.
power-splitting transmission (PST)
A type of hybrid transmission that splits the power flow going to the wheels from one or more electric motors and an internal combustion engine.
prechamber
A separate combustion area designed into a diesel cylinder head.
preload
Further pressure applied to bearing-supported parts after all the free play is taken up.
preloaded
The level of pressure placed on bearings that ensures the bearings will be held together.
press-fit pin
A description of how a piston pin is placed inside a connecting rod by pressing the pin into the connecting rod.
pressure bleeding
A bleeding method that uses clean brake fluid under pressure from an auxiliary tool or piece of equipment to force the air and old brake fluid from the hydraulic braking system.
pressure differential valve
A valve that monitors any pressure difference between the two separate hydraulic brake circuits; it usually contains a switch to turn on the brake warning light when there is a pressure difference.
pressure
The force per unit area applied to the surface of an object.
pressure gauge set
A set of calibrated gauges for high and low pressure that can show pressure and vacuum readings for use with air-conditioning systems.
pressure plate
The assembly that applies and removes the clamping force on the clutch disc.
pressure relief valve
A valve that is designed to release pressure if it gets above a calibrated pressure; used in a gas cap as a safety device to release excessive pressure if pressure gets too high.
pressure transducer
A device used to measure engine vacuum and display it graphically on a lab scope.
pressure transients
Minor fluctuations on the gauges that may indicate a problem.
pressure washer/cleaner
A cleaning machine that boosts low-pressure tap water to a high-pressure output.
pressure, or force-feed, lubrication system
A lubrication system that has a pump to pressurize the lubricating oil and push it through the engine to moving parts.
pressure testing
A process for checking the aluminum cylinder heads for cracks using air pressure.
Pressure washers and cleaners
A cleaning machine that boosts low-pressure tap water to a high-pressure output.
prick punch
A pinch with a sharp point for accurately marking a point on metal.
primary cup
A seal that holds pressure in the master cylinder when force is applied to the piston.
primary piston
A brake piston in the master cylinder moved directly by the pushrod or the power-booster; it generates hydraulic pressure to move the secondary piston.
primary winding
The coil of wire in the low voltage circuit that creates the magnetic field in a step-up transformer.
primary circuit
The low-voltage circuit that turns the coil on and off.
Printed circuits
The fine copper strip or track attached to an insulated board for mounting and connecting electronic components.
printed circuitry
Circuitry that forms the framework for electronic module construction. A printed circuit board holds electronic components that are soldered into place.
probing technique
The way in which test probes are connected to a circuit.
procedure
A list of the steps required to get the same result each time a task or activity is performed.
producer gas
A generic term that refers to a number of manufactured gases such as wood gas, town gas, and syngas.
programmed fuel delivery map
A chart programmed into the vehicle’s computer that is referenced as the vehicle is running. Sensor input data are compared to the delivery map to calculate the desired output signal.
progressive rate of deflection
The change in deflection rate that occurs as the weight of the vehicle changes. The greater the weight, the lower the rate of deflection due to increased resistance.
proportioning valves
Valves used mostly on older vehicles equipped with rear drum brakes to reduce rear wheel hydraulic brake pressure under hard braking or light loads. Located in line with the rear brakes.
propylene glycol
A chemical used as anti-freeze. It is labeled as a nontoxic anti-freeze.
propylene-glycol
A chemical used as anti-freeze. It is labeled as a nontoxic anti-freeze.
pry bars
A high-strength carbon steel rod with offsets for levering and prying.
pry bar
A high-strength carbon steel rod with offsets for levering and prying.
pull-in winding
A high-current winding found in starter solenoids that pulls the solenoid plunger into the activated position.
pullers
A generic term to describe hand tools that mechanically assist the removal of bearings, gears, pulleys, and other parts.
pulse air system
The use of normal exhaust engine pulses to draw air into the exhaust stream.
pulse width modulation
A digital on/off electrical signal used as a variable control for devices such as solenoids.
pulse width modulation (PWM)
A digital on/ off electrical signal used as a variable control for devices such as solenoids.
pulse-width modulation (PWM)
A digital on/off electrical signal used as a variable control for devices such as solenoids.
pulse-width modulation (combustion)
The time that the fuel injectors are turned off and on to inject a precise amount of fuel.
pulse-width modulation
A digital on/off electrical signal used as a variable control for devices such as solenoids.
punches
A generic term to describe a highstrength carbon steel shaft with a blunt point for driving. Center and prick punches are exceptions and have a sharp point for marking or making an indentation.
purge solenoid
A control device that lets fuel vapors move from the charcoal canister to the engine. The solenoid is controlled by the engine control module.
purge switch
A device used to show the computer when purge is occurring. It is used as a feedback device to allow the computer to determine whether flow is happening
purge valve
A valve used to control the flow of evaporative emissions from the charcoal canister to the intake manifold.
purging
The process of pulling stored fuel vapors from the charcoal canister and moving them into the engine to be burned.
push-on spade terminals
A disconnectable type of crimp or solder terminal used to terminate electrical wires.
push-on spade terminal
A disconnectable type of crimp or solder terminal used to terminate electrical wires.
push-type clutch
A typical clutch system used in modern vehicles where the clutch fork pushes the release bearing forward to release the friction facing from the pressure plate.
pushrod (braking system)
A mechanism used to transmit force from the brake pedal to the master cylinder.
pushrod
A long, thin cylindrical shaft that provides a linkage between the lifters and the rocker arms to control valve opening and closing.
pushrods
A long, thin cylindrical shaft that provides a linkage between the lifters and the rocker arms to control valve opening and closing.
Q
quadrant ratchet
The device used in some cable operated clutches to provide self-adjustment as the clutch disc wears. Some quadrant ratchets adjust if you lift up on the clutch pedal.
quench or squish area
The narrow area between the top of the piston at top dead center and the cylinder head. It derives its name from the squishing of the air/fuel mixture into a small “charge.”
quenched
The state in a combustion chamber in which the flame cannot burn due to cold surfaces or poor distribution of the fuel mixture.
quick take-up valve
A valve used to release excess pressure from the larger piston in a quick take-up master cylinder once the brake pads have contacted the brake rotors.
quick take-up master cylinders
Cylinders used on disc brake systems that are equipped with low-drag brake calipers to quickly move the brake pads into contact with the brake rotors.
R
rack
A steel rod driven by the pinion with tie-rods on each end or tie-rods connected to the center of the rack.
rack housing
The outer shell of the rack-and-pinion steering system that is mounted to the chassis.
rack-and-pinion steering system
A steering system composed of a steering wheel, a main shaft, universal joints, and an intermediate shaft. When the steering wheel is turned, movement is transferred by the main shaft and intermediate shaft to the pinion.
radial
A tire with two or more layers of casing plies and cord loops running radially from bead to bead.
radial loads
The load that is perpendicular to a shaft, usually controlled by bearings or bushings.
radial tire
A tire with two or more layers of casing plies and cord loops running radially from bead to bead.
radial load
The load that is perpendicular to a shaft, usually controlled by bearings or bushings.
radiation
The transfer of heat through the emission of energy in the form of invisible waves.
radiator
A device that takes hot coolant and cools it by passing heat energy to the surrounding air.
radiator hoses
Rubber hoses that connect the radiator to the engine. Because they are subject to pressure, they are reinforced with a layer of fabric, typically nylon.
radius
A straight line extending from the center of a circle to its edge or from the center of a sphere to its surface.
ram airflow
The flow of air created by a vehicle moving down the road.
raster
The scope pattern where all of the ignition firing sequences are stacked vertically on top of each other.
ratchet
A generic term to describe a handle for sockets that allows the user to select direction of rotation. It can turn sockets in restricted areas without the user having to remove the socket from the fastener.
ratcheting box-end wrench
A wrench with an inner piece that is able to rotate within the outer housing, allowing it to be repositioned without being removed.
ratcheting screwdriver
A screwdriver with a selectable ratchet mechanism built into the handle that allows the screwdriver tip to ratchet as it is being used.
rattle gun
A term used describe an air impact wrench based on the noise it makes.
Ravigneaux gear set
A type of compound planetary gear set that uses two different sun gears and two different-diameter planets while only using one ring gear.
reaction force
A force that acts in the opposite direction to another force.
rear-wheel drive (RWD)
A drive train layout in which the engine drives the rear wheels.
rebound clips
A metal strap that is warped around the leaf spring to prevent excessive flexing of the main leaf during rebound.
rebound clip
A metal strap that is warped around the leaf spring to prevent excessive flexing of the main leaf during rebound.
receiver filter drier (RFD)
The air-conditioning component used on TXV systems to filter and store liquid refrigerant to supply liquid refrigerant to the TXV. It is located between the condenser and the TXV.
reciprocating motion
An up-and-down motion within the cylinder.
reciprocating weight
The amount of weight that is moving up and down. It is everything from the middle of the connecting rod upward, including the piston, wrist pin, and rings.
reciprocating
The back-and-forth movement of the piston assembly inside the cylinder.
reciprocation
The back-and-forth movement of the piston assembly inside the cylinder.
recirculating ball steering box
A steering box that has worm gear inside a block with a threaded hole in it and gear teeth cut into its outside that engage the sector shaft to move the pitman arm; generally used on trucks and heavy vehicles.
reclaim/recycle machine
An air-conditioning machine designed to remove and recycle refrigerant for reuse.
reclaiming
The process of removing refrigerant from the air-conditioning system by using an air-conditioning machine; also called recovering.
recovering
The process of removing refrigerant from the air-conditioning system by using an air-conditioning machine; also called recovering.
rectification
A process of converting AC into DC required by the battery and nearly all of the automobile systems.
recuperation
Process by which brake fluid moves from the reservoir past the edges of the seal into the chamber in front of the piston. This prevents air from being drawn into the hydraulic system caused by low pressure when the brake pedal is released quickly.
reductant
A reducing agent.
reduction ratio
The ratio between the turn of the steering wheel and the turn of the wheel, both measured in degrees.
reed switch
A type of speed sensor that uses a magnetic field to open and close a movable set of contacts. It is used with a rotating magnet to measure rpm of a shaft and send the signal to the PCM.
reed valve
A flexible valve made from spring steel that flexes to open or close, usually due to pressure changes.
reformer
An on-board device that extracts hydrogen from another source material.
refrigerant
The name given to a chemical compound designed to meet the needs of the refrigeration system.
refrigerant identifiers
Devices used to check for impurities in the air-conditioning system.
refrigerant label
A label that lists the type and total capacity of refrigerant that is installed in the A/C system.
regenerative braking
Technology used in vehicles that allows the vehicle to recapture and store part of the vehicle’s kinetic energy in a reusable form when braking. Primarily used in hybrid and electric vehicles.
relay
An electromechanical switching device whereby the magnetism from a coil winding acts on a lever that switches a set of contacts.
relay lever
A steel rod that transfers movement from the drag link to an idler arm.
release mechanisms
Components that operate the clutch. Usually included are the throw-out bearing and the clutch fork. Some manufacturers include the operating system.
release mechanism
Components that operate the clutch. Usually included are the throw-out bearing and the clutch fork. Some manufacturers include the operating system.
reluctor
A rotating, toothed wheel that changes the reluctance of a material to conduct magnetic lines of force.
remote keyless entry (RKE)
A system that remotely unlocks and locks the vehicle without the use of a traditional key.
repair order
A form used by shops to collect information regarding a vehicle coming in for repair, also referred to as a work order.
required voltage
The amount of voltage needed to push current across the electrodes of a spark plug located in the combustion chamber.
reserve capacity
A standard used to specify the time in minutes that a battery will supply a load of 25 amps at 80°F (27°C) without its voltage dropping below 10.5 volts.
residual pressure valve
(residual check valve) In drum brake systems, a valve that maintains pressure in the wheel cylinders slightly above atmospheric pressure so that air does not enter the system through the seals in the wheel cylinders.
resistor
A component designed to have a fixed resistance.
resistor in series
A resistor added to the circuit before or after the load to drop voltage to the load.
resistors in series
A resistor added to the circuit before or after the load to drop voltage to the load.
respirator
Protective gear used to protect the wearer from inhaling harmful dusts or gases. Respirators range from single-use disposable masks to types that have replaceable cartridges. The correct types of cartridge must be used for the type of contaminant encountered.
restriction
A blockage that partially stops or slows the flow of a material such as refrigerant.
retarding effect
The result of retarding (slowing) the vehicle.
retrofit kit
An aftermarket kit that has the fittings and oil to change an R-12 unit over to an R-134a unit.
return springs
Springs that retract the brake shoes to their released position.
returnless fuel injection systems
A type of injection system in which no hot fuel is returned to the tank, thus keeping the fuel in the tank relatively cool and minimizing vaporization.
returnless fuel injection system
A type of injection system in which no hot fuel is returned to the tank, thus keeping the fuel in the tank relatively cool and minimizing vaporization.
reverse boost valve
A component of the pressure regulator valve that increases line pressure when the vehicle is in reverse.
reverse shift fork
A shift fork used to engage the reverse gear.
rheostat
An adjustable resistor that varies current flow through a circuit.
rib
A design feature created in the metal casting/forging process that places extra metal area on a part for strength and durability, yet keeps the weight of the engine block low.
ribbon cable
A type of flat harness in which cables are insulated from each other but joined together side by side.
ribs
A design feature created in the metal casting/forging process that places extra metal area on a part for strength and durability, yet keeps the weight of the engine block low.
ridge reamer
A tool used to remove the metal lip on top of the cylinder walls caused by engine wear.
rigid nondrive axle suspension
A type of dead axle suspension system that is non-independent and uses a beam or solid axle.
rigid spring hanger
The rigid part typically welded to the body or frame of the vehicle to which the front of the leaf spring is attached.
rigid non-drive axle suspension
A type of dead axle suspension system that is non-independent and uses a beam or solid axle.
rigid non drive axle suspension
A type of dead axle suspension system that is non-independent and uses a beam or solid axle.
rigid-axle coil-spring suspensions
A dead axle that uses a coil spring.
rigid-axle coil-spring suspension
A dead axle that uses a coil spring.
rim
The outer circular lip of the metal on which the inside edge of the tire is mounted.
rim flanges
The outside edge of the wheel that helps keep the tire from popping off the wheel.
rim width
The distance across the rim from one rim flange to the other.
ring gap
The distance between the ends of the piston rings when the rings are seated against the inside of the engine cylinder.
ring gear
A large circular gear that is typically mounted on the flywheel or flex plate and mates to the starter gear, for the purpose of cranking the engine over.
ring lands
The metal between the ring grooves that supports the rings as the piston moves.
ring tension
The built-in force created inside the piston rings due to the fact that the piston rings are made bigger than the cylinder walls to generate a scraping action against the cylinder walls.
rising characteristic
A characteristic at a fixed fuel setting where the amount of fuel delivered to the engine will increase as engine speed and pump speed increase.
riveted linings
Brake linings riveted to the brake pad backing plate with metal rivets and used on heavier duty or high-performance vehicles.
rocker arm
A lever that actuates a valve by pivoting near the center and pushing on the tip of the valve to open it.
rocker arms
A lever that actuates a valve by pivoting near the center and pushing on the tip of the valve to open it.
rod bearing
A bearing insert located in the big end of the connecting rod.
rod beam
The area of connecting rod between the big and small ends.
rod bearings
A bearing insert located in the big end of the connecting rod.
rod bearing journals
A bearing surface that is offset from the center line of the crankshaft.
rod cap
The very bottom part of the connecting rod that retains the rod bearing inserts.
rod journal
Also called the crankshaft rod throw, an area machined to a very smooth finish that contains an oil hole to provide oil to lubricate the surfaces of the crankshaft and rod bearing inserts.
rod bearing journal
A bearing surface that is offset from the centerline of the crankshaft.
rod
A straight piece of steel used to transfer motion within the vehicle’s suspension system. It typically has treads cut on one or both ends.
rods
A straight piece of steel used to transfer motion within the vehicle’s suspension system. It typically has treads cut on one or both ends.
roll
Movement of a vehicle around its x-axis (the imaginary line down the center of the vehicle from front to back). It is commonly referred to as body roll or lean; when cornering, the body will try to move to the outside of the corner against the suspension.
roll bar
Another type of pry bar, with one end used for prying and the other end for aligning larger holes, such as engine motor mounts.
roll-rate sensor
A sensor that measures the amount of roll around the vehicle’s horizontal axis that a vehicle is experiencing.
roller bearings
A long cylindrical roller held in position by a cage.
roller bearing
A long cylindrical roller held in position by a cage.
rolling code
A constantly changing, randomly selected numeric code that is communicated with the engine immobilizer and security system.
rolling resistance
Resistance that is present from tires contacting the road and wind resistance against the vehicle while rolling down the highway.
room temperature vulcanizing (RTV) silicone
A silicone adhesive that sets up or “vulcanizes” at room temperature.
rosin
A type of liquid or paste (flux) used to prevent oxidization that is in solid form contained within the solder.
rotary engines
An engine that uses a triangular rotor turning in a housing instead of conventional pistons.
rotary flow
A type of fluid flow in a torque converter in which fluid flows around the center line of the torque converter in a circle.
rotary vane compressors
A compressor design that spins with vanes attached that extend to create the air-conditioning pressure required to run the system.
rotary engine
An engine that uses a triangular rotor turning in a housing instead of conventional pistons.
rotary vane compressor
A compressor design that spins with vanes attached that extend to create the air-conditioning pressure required to run the system.
rotating assembly
The assembly of the crankshaft, connecting rod, and piston that are found inside the engine cylinder block.
rotating weight
The amount of weight that is moving in a circular motion, including everything from the center of the connecting rod down to the connecting rod cap and all components of the crankshaft.
rotational force
The force created by the rotating wheel when the brakes are applied; it causes the brake components to twist the brake support and ultimately the vehicle in the direction of wheel rotation.
rotational speed
The speed at which an object rotates, measured in revolutions per minute (rpm).
rotor (brakes)
The main rotating part of a disc brake system.
rotor (engine)
A high-voltage rotating switch that transfers voltage from the distributor cap’s center terminal to the outer terminals.
rotor arm
The portion of the rotor that extends toward, but not touching, the outer distributor cap terminals.
rotor housing
The engine block of the rotary engine. The rotor moves within it.
rotor lobes
Lobes or rounded edges on rotors that squeeze oil and create pressure.
rotor pump
A type of front pump found in automatic transmissions. The rotor pump has two different-sized rotors that mesh together to force fluid out of the pump.
rotor
A high-voltage rotating switch that transfers voltage from the distributor cap’s center terminal to the outer terminals.
rotor-type oil pump
An oil pump that uses rounded gears to squeeze oil through.
rotors
A high-voltage rotating switch that transfers voltage from the distributor cap’s center terminal to the outer terminals.
rubber bellows
Rubber pieces positioned on each end of the rack to protect the inner joints from dirt and contaminants and retain the grease lubricant inside the rack-and-pinion housing.
rubber-bonded bushings
A bushing that has a steel outer housing and inner sleeve with rubber inside; also known as a metalastic bushing.
rubber-bonded bushing
A bushing that has a steel outer housing and inner sleeve with rubber inside; also known as a metalastic bushing.
run-flat technology
A tire design that allows the vehicle to keep moving under driver control following a puncture or rapid loss of pressure.
running clearance
The amount of space between wheel bearing components while in operation.
Rzeppa joint
A type of fixed constant velocity joint that has an inner race, six steel ball bearings, a bearing cage, and an outer race.
S
SAE J1930
An SAE standard for across-the-board standardization of parts and systems nomenclature.
SAE J2012
An SAE standard for across-the-board identification of generic DTCs.
safe working load (SWL)
The maximum safe lifting load for lifting equipment.
safety-type drop-center rims
A rim designed with a slight hump at the inside edge of the bead ledges to hold the tire beads in place during a flat tire.
safety-type drop-center rim
A rim designed with a slight hump at the inside edge of the bead ledges to hold the tire beads in place during a flat tire.
salvage title
Also called a branded title; a record that a vehicle has been severely damaged or deemed a total loss by an insurance company.
sand or bead blasters
A cleaning system that uses high-pressure fine particles of glass bead or sand.
Sanden scroll-type compressor
A compressor design that uses two spiral forms, one spinning and one stationary, to create the pressure needed to drive the air-conditioning system.
Sanden wobble plate compressor
A compressor design that utilizes an offset shaft connected to the crankshaft to create the reciprocating motion of the pistons.
sander/polisher
A power tool with a rotating disc or head to which polishing or sanding discs can be attached.
scan tool
A plug-in electronic device for extracting and interpreting fault codes (DTCs) in the automobile, plus much more.
scan tools
A plug-in electronic device for extracting and interpreting fault codes (DTCs) in the automobile, plus much more.
scavenge pump
A pump used with a dry sump oiling system to pull oil from the dry sump pan and move it to an oil tank outside the engine.
scavenging
The removal of hot exhaust gases fro the cylinder and the refilling of it with fresh air.
scavenging effect
A condition caused by moving columns of air, which create a low-pressure area behind them, resulting in a pulling force that is used to pull the remaining burned gases from the combustion chamber. Valve timing affects the amount of scavenging effect an engine has.
Schrader valve
A one-way valve used in a valve stem.
scratcher
A thin, spring steel wear indicator that is fixed to the backing plate of the brake pad; it emits a high-pitched squeal when the brakes are applied if the brake pads have become too thin.
screw extractors
A tool for removing broken screws or bolts.
screw extractor
A tool for removing broken screws or bolts.
scrub brakes
A brake system that uses leverage to force a friction block against one or more wheels.
scrub radius
The distance between two imaginary points on the road surface—the point of center contact between the road surface and the tire, and the intersecting point where the steering axis centerline and the tire centerline contact the road surface.
sealed bearings
Wheel bearings that are assembled by the manufacturer with the proper lubrication and sealed for life; cannot normally be disassembled.
second-degree burns
Burns that involve blistering and damage to the outer layer of skin.
second-order vibration
Vibration that occurs at twice the engine rpm.
secondary cup
A seal that prevents loss of fluid from the rear of each piston in the master cylinder.
secondary piston
A piston that is moved by hydraulic pressure generated by the primary piston in the master cylinder.
secondary winding
The high-voltage copper wiring found in an ignition coil.
secondary circuit
The part of an ignition system that operates on higher voltage and delivers the necessary high voltage to the spark plugs.
sedan
A vehicle configuration that has an enclosed body, with a maximum of four doors to allow access to the passenger compartment.
selective catalytic reduction
An active emission control system that injects a liquid reductant, or reducing agent, through a special catalyst into the exhaust stream of a diesel engine.
selective thickness shims
A shim of a prescribed thickness that is used to control shaft clearances in a transmission.
selective thickness shim
A shim of a prescribed thickness that is used to control shaft clearances in a transmission.
selector gate
The U-shaped cutaway in shift shafts that the shifter lever fits into.
selector shift rail
A rod that is attached to the shift fork. These rails move when the shifter lever is moved against them.
self-energizing
The property of drum brakes that assists the driver in applying the brakes; when brake shoes come into contact with the moving drum, the friction tends to wedge the shoes against the drum, thus increasing the braking force.
self-leveling
A vehicle with automatic load-adjustable shock absorbers.
self-sealing tires
A tire constructed with a flexible and malleable lining inside the tire around the inner tubeless membrane. The lining can seal small tread-area punctures instantly and permanently.
self-sealing tire
A tire constructed with a flexible and malleable lining inside the tire around the inner tubeless membrane. The lining can seal small tread-area punctures instantly and permanently.
semi-floating axle
An axle that carries the weight of the vehicle; if removed, there is no way to connect the wheel to the vehicle.
semiautomatic climate control system
A system that provides automatic function of the heater or cooling only, leaving fan speed and mode selection to the operator.
semiautomatic
A system that provides automatic function of the heater or cooling only, leaving fan speed and mode selection to the operator.
semiconductor
A material used to make microchips, transistors, and diodes.
sending unit
The component in the fuel supply system responsible for sending constant electrical signals to the gas gauge located in the driver information center.
separator PCV system
A PCV system that uses a device that uses gravity to allow oil to fall to the bottom of the valve and be returned to the crankcase; the valve prevents liquid from traveling to the intake manifold.
separator plate
Sometimes called a spacer plate, a thin sheet metal plate installed between the valve body and the transmission case. Orifices can be installed in the separator plate, and check valves can work with holes in the plate.
separator
A PCV system that uses a device that uses gravity to allow oil to fall to the bottom of the valve and be returned to the crankcase; the valve prevents liquid from traveling to the intake manifold.
series hybrid
A hybrid electric vehicle powered by an internal combustion engine, but driven by battery.
series hybrid drive train
A type of hybrid transmission in which power flows from the engine through an electric motor. The electric motor supplements the power from the engine to the wheels.
series-parallel circuit
A circuit that has both a series and a parallel circuit combined into one circuit.
series-parallel hybrid
A hybrid electric vehicle that uses the internal combustion engine and/or the battery pack for propulsion.
series-parallel hybrid drive train
A type of hybrid drive train that can function as both a series hybrid and parallel hybrid. That means the gasoline engine can turn a generator that can be used to power an electric motor. The gasoline engine can also drive the vehicle directly through the transmission. And the electric motor can work in parallel with the gasoline engine to drive the vehicle.
serpentine condensers
A condenser with one tube snaking back and forth.
serpentine condenser
A condenser with one tube snaking back and forth.
service brake
A brake system that is operated while the vehicle is moving to slow or stop the vehicle.
service campaign and recall
A corrective measure conducted by manufacturers when a safety issue is discovered with a particular vehicle.
service consultants (advisors)
A service worker who works with both customers and technicians; the first point of contact for customers seeking vehicle repairs.
service history
A complete list of all the servicing and repairs that have been performed on a vehicle.
service managers
The shop supervisor who is responsible for the management of the service department.
Service campaigns and recalls
A corrective measure conducted by manufacturers when a safety issue is discovered with a particular vehicle.
service consultant/advisor
A service worker who works with both customers and technicians; the first point of contact for customers seeking vehicle repairs.
service manager
The shop supervisor who is responsible for the management of the service department.
serviceable bearings
Wheel bearings that can be disassembled, cleaned, inspected, packed, reinstalled, and adjusted.
servo action
A drum brake design where one brake shoe, when activated, applies an increased activating force to the other brake shoe, in proportion to the initial activating force; further enhances the self-energizing feature of some drum brakes.
servo
A hydraulic device consisting of a piston inside a cylinder that is used to apply a band. The servo also has a spring that releases the servo when it is no longer needed.
servos
A hydraulic device consisting of a piston inside a cylinder that is used to apply a band. The servo also has a spring that releases the servo when it is no longer needed.
setback
The distance one wheel is set back from the wheel on the opposite side of the axle.
shaft
The long, narrow component that carries one or more gears or has gears machined into it.
shafts
The long, narrow component that carries one or more gears or has gears machined into it.
shielded wiring harnesses
A wiring harness that has shielding built into it to protect it from induced electrical interference.
shielded wiring harness
A wiring harness that has shielding built into it to protect it from induced electrical interference.
shift forks
A mechanism that moves the synchronizer sleeve to lock the gear to the main shaft.
shift solenoid
An electromechanical device used to control oil flow to bands and clutches in an automatic transmission to help shift the transmission.
shift valve
A type of spool valve that has multiple fluid inputs and a spring; it is used to direct hydraulic pressure to a clutch or band needed for a shift.
shift fork
A mechanism that moves the synchronizer sleeve to lock the gear to the main shaft.
shift valves
A type of spool valve that has multiple fluid inputs and a spring; it is used to direct hydraulic pressure to a clutch or band needed for a shift.
Shift solenoids
An electromechanical device used to control oil flow to bands and clutches in an automatic transmission to help shift the transmission.
shock
Inadequate tissue oxygenation resulting from serious injury or illness.
shock absorbers
A device on a vehicle designed to absorb bumps and jolts caused from driving on irregular surfaces and to dampen body movement.
shock absorber
A device on a vehicle designed to absorb bumps and jolts caused from driving on irregular surfaces and to dampen body movement.
shop foreman
The supervisor in a shop who oversees the work of technicians and staff and communicates with customers and external suppliers.
shop or service manuals
Manufacturer’s or aftermarket information on the repair and service of vehicles.
shop or service manual
Manufacturer’s or aftermarket information on the repair and service of vehicles.
short circuits
A condition in which the current flows along an unintended route.
short to power
A condition in which current flows from one circuit into another.
short
Also called a short circuit, the flow of current along an unintended route.
short block
An engine assembly that includes the engine block, camshaft, timing set, pistons, rods, and crankshaft installed.
short circuit
A condition in which the current flows along an unintended route.
short-/long-arm (SLA) suspension
A type of control arm suspension system that uses a short control arm on the top and a long control arm on the bottom. This design ensures correct alignment angles when moving through bumps.
shroud
A steel or plastic cover placed over the shock rod.
side force
The pressure on the wheel that pushes it toward the outside or inside of the rim as the vehicle makes a turn.
side gear
A gear that is splined to the axle shaft and meshes with the spider gears and allows the axles to rotate at their own speeds when cornering and turning.
side rails
The thin portion of the oil control ring that is used to scrape oil off of the cylinder walls.
side rail
The thin portion of the oil control ring that is used to scrape oil off of the cylinder walls.
side gears
A gear that is splined to the axle shaft and meshes with the spider gears and allows the axles to rotate at their own speeds when cornering and turning.
signal voltage values
Measured voltage in a signal return circuit that is compared to a specified voltage value published by the manufacturer.
signal voltage value
Measured voltage in a signal return circuit that is compared to a specified voltage value published by the manufacturer.
silicon carbide
A type of material used to make semiconductors.
silicon
A material commonly used to make semiconductors.
simple fracture
A fracture that involves no open wound or internal or external bleeding.
Simpson gear set
A type of gear set with two planetary gear sets that share a common sun gear.
sine wave
A mathematical function that describes a repetitive waveform such as an alternating current signal.
single flare
A sealing system made on the end of metal tubing.
single-piston master cylinders
A master cylinder with a single piston that creates hydraulic pressure for all wheel units. If there is a leak in the system, there is a loss of pressure for all wheel units.
single-piston master cylinder
A master cylinder with a single piston that creates hydraulic pressure for all wheel units. If there is a leak in the system, there is a loss of pressure for all wheel units.
single-plate clutch
A clutch assembly that uses only one plate to transfer torque from the engine to the transmission. This is the most common type of light vehicle clutch.
single-post hoist
A type of vehicle hoist that uses a single central platform to lift a vehicle.
sintered
The process of using pressure and heat to bond metal particles.
sintering process
A metal hardening process in which the metal is fused together without melting.
sintering
The process of using pressure and heat to bond metal particles.
slave cylinder
The component in a hydraulically operated clutch that converts hydraulic pressure to mechanical movement at the clutch fork.
sledge hammer
A heavy hammer, usually with two flat faces, that provides a strong blow.
sliding or floating calipers
A type of brake caliper that only has piston(s) on the inboard side of the rotor. The caliper is free to slide or float, thus pulling the outboard brake pad into the rotor when braking force is applied.
sliding or floating caliper
A type of brake caliper that only has piston(s) on the inboard side of the rotor. The caliper is free to slide or float, thus pulling the outboard brake pad into the rotor when braking force is applied.
sliding spline driveshaft
A two-piece driveshaft that is joined in the middle with splines. The driveshaft can slide on itself to increase or decrease in length.
sliding T-handle
A handle fitted at 90 degrees to the main body that can be slid from side to side.
slip angle
A tire’s sideways distortion that makes the vehicle follow a path at an angle to the direction the road wheel is pointing.
slip yoke
Part of a two-piece driveshaft that is splined and allows for a change in length of the shaft as the suspension compresses and rebounds.
slippage
A condition in which two surfaces in firm contact with each other slide.
slow chargers
A battery charger that charges at low current.
slow charger
A battery charger that charges at low current.
slow-fill
The method of filling a compressed natural gas vehicle (such as overnight) so the cylinders are completely filled.
smart chargers
A battery charger with microprocessor-controlled charging rates and times.
smart charger
A battery charger with microprocessor-controlled charging rates and times.
snap ring pliers
A pair of pliers for installing and removing snap rings or circlips.
snap rings
The spring-steel C-shaped ring that is fitted in a groove and holds gears, bearings, and shafts in place.
snap ring
The spring-steel C-shaped ring that is fitted in a groove and holds gears, bearings, and shafts in place.
sniffer
An electronic device used to determine the source of leaks.
sniffers
An electronic device used to determine the source of leaks.
socket
An enclosed metal tube commonly with 6 or 12 points to remove and install bolts and nuts.
soft plugs
A thin-walled, metal, cup-shaped disc designed to be pressed into a machined passageway in the block for the purpose of plugging it.
soft plug
A thin-walled, metal, cup-shaped disc designed to be pressed into a machined passageway in the block for the purpose of plugging it.
solder
A mixture of lead and tin with a low melting point for connecting wires.
solder-type terminals
A terminal that requires soldering to fasten the terminal to the cable or wire.
solder-type terminal
A terminal that requires soldering to fasten the terminal to the cable or wire.
soldering iron
A heating tool to heat solder and wires to produce a low-resistance joint.
soldering irons
A heating tool to heat solder and wires to produce a low-resistance joint.
solenoid valves
An electrically operated valve that when used in brake systems is designed to control the flow of brake fluid in the hydraulic system.
solenoid
An electromagnet with a moving iron core that is used to cause mechanical motion.
solenoid valve
An electrically operated valve that when used in brake systems is designed to control the flow of brake fluid in the hydraulic system.
solid rotors
A type of brake rotor made of solid metal.
solid axle
A single piece of steel that provides a simple means of mounting the hub and wheel units. Also called beam axle or straight axle.
solid rear axle
A type of axle that has a one-piece axle housing, so that the action of hitting a bump with one wheel affects the other wheel.
solid rotor
A type of brake rotor made of solid metal.
solid valve lifter
A non-hydraulic valve lifter.
solid valve lifters
A non-hydraulic valve lifter.
solid-state relay
A relay that performs the function of a mechanical relay but using only electronic components.
solvent tank
A tank containing solvents to clean vehicle parts.
spark ignition (SI) engines
An engine that relies on an electrical spark to ignite the air and fuel mixture.
spark line
The horizontal line immediately after the firing line on an ignition pattern. It shows how much voltage and the length of time the spark is burning.
spark plug
A device that provides a gap for the high-voltage spark to occur in each cylinder.
spark plug reach
The length of the spark plug from the seat to the end of the threads.
spark timing
The point at which a spark occurs at the spark plug relative to the position of the piston.
spark ignition (SI) engine
An engine that relies on an electrical spark to ignite the air and fuel mixture.
specialty springs
Springs used to return links and levers on the parking brake system or the self-adjuster mechanism.
speed control circuits
A circuit that controls the speed of a motor.
speed brace
A U-shaped socket wrench that allows high-speed operation. Also called a speeder handle.
speed sensor
A sensor responsible for measuring the speed of the vehicle that is read by the speedometer.
speed sensor (VSS)
A sensor used by the PCM to measure vehicle speed. It is often located in the transmission extension housing.
speed control circuit
A circuit that controls the speed of a motor.
speedy sleeve
An aftermarket repair kit that consists of a thin metal sleeve that fits tightly over the seal surface of the axle, providing a new, undamaged surface for the seal to ride against.
splash lubrication
A lubrication system that relies on oil being splashed onto moving parts by rotating engine parts striking the oil. These systems are typically used in small engines.
spline
A ridge or tooth on a driveshaft that meshes with grooves in a mating piece and transfers torque to it, maintaining the angular correspondence between them.
splined section
A flat key made into a shaft to accommodate changes in shaft length due to movement in wheel camber with suspension action.
splined torsional dampening center hub
The center portion of a clutch disc that splines to the input shaft. It also incorporates a spring-loaded damper that absorbs engine pulsations for a smoother ride.
splined
Typically, a shaft and gear that have parallel grooves machined in them so they mate with each other and lock together rotationally.
split diagonally
A brake system in which the left front wheel is hydraulically paired with the right rear wheel and the right front wheel is paired with the left rear. This preserves 50% of the braking capability if one of the brake circuits begins to leak.
split front to rear
A brake system in which the front brakes operate on one hydraulic circuit and the rear brakes from the other.
split ball gauge
A measuring device used to accurately measure small holes.
spool valve
A type of valve commonly used in automatic transmissions that resembles the spool that thread or fishing line comes on.
sport utility vehicle (SUV)
A passenger vehicle built on a light-truck chassis; it is usually equipped with four-wheel drive and capable of hauling heavier loads than typical passenger vehicles.
Sport utility vehicles (SUVs)
A passenger vehicle built on a light-truck chassis; it is usually equipped with four-wheel drive and capable of hauling heavier loads than typical passenger vehicles.
sprain
An injury in which a joint is forced beyond its natural movement limit.
spray wash cabinets
A cleaning cabinet that sprays cleaning solution under pressure to clean vehicle parts.
spray wash cabinet
A cleaning cabinet that sprays cleaning solution under pressure to clean vehicle parts.
spring eyes
Rolled ends of some springs used to mount springs to the chassis.
spring pressure
Pressure exerted by a metal coil usually measured in pounds.
spring shackle bushings
A bushing that is positioned in the shackle that the leaf spring mounts to. Bushings allow the spring shackle to move as the leaf spring dimensions change over bumps.
spring shackle bushing
A bushing that is positioned in the shackle that the leaf spring mounts to. Bushings allow the spring shackle to move as the leaf spring dimensions change over bumps.
spring
A resilient steel part that stores energy when compressed and releases energy when released to its original state; available as a leaf spring, coil spring, or torsion bar.
spring-loaded keys
A part of the synchronizer that helps hold the synchronizer collar in position.
spring-loaded rack guide yoke
A spring-containing part that pushes on the back side of the rack to help reduce the play between the rack and the pinion while still allowing for relative movement.
spring-loaded key
A part of the synchronizer that helps hold the synchronizer collar in position.
springs and clips
Various devices that hold the brake shoes in place or return them to their proper place.
springs
A resilient steel part that stores energy when compressed and releases energy when released to its original state; available as a leaf spring, coil spring, or torsion bar.
spur gears
A type of gear in which the teeth of the gear are cut in a straight line down the axis of the gear.
spur gear
A type of gear in which the teeth of the gear are cut in a straight line down the axis of the gear.
square cut O-ring
An O-ring with a square cross-section that is used to seal the pistons in disc brake calipers.
square file
A type of file with a square cross section.
square threads
A thread type with square shoulders used to translate rotational to lateral movement.
square thread
A thread type with square shoulders used to translate rotational to lateral movement.
squib
The component inside the airbag inflator that triggers the airbag deployment.
staged governor
A governor in which the assembly uses two valves: a primary valve and a secondary valve.
stall
Often referred to as stall speed, the maximum rpm difference between the turbine and the impeller in the torque converter.
stall test
A test that involves raising the engine rpm to wide-open throttle while the brake is firmly applied and the transmission is in gear. The test is used to check torque convertor and transmission operation on some vehicles.
standard torque converter
A hydraulic coupling device consisting of an impeller, turbine, stator, and housing; located between the engine and the transmission.
starter teeth
Machined teeth located on the ring gear for meshing with the starter drive teeth located in the starter motor.
state of charge
The amount of refrigerant in a system compared to how much should be in it.
static imbalance
A tire imbalance resulting from a heavy spot on a tire; it will vibrate vertically with the heavy area slapping the road surface with each turn of the wheel.
static toe
A setting designed to compensate for slight wear in steering components that may cause the wheels to turn outward or inward while the vehicle is in motion.
station wagon
A vehicle configuration with four doors with a roof line that continues into the rear cargo area and a rear door for access.
stationary winding
An extended length of wire wrapped into a circle. These windings are fixed as opposed to some types, which are meant to spin.
stator
Portion of an electronic ignition system that is mounted to the base of the distributor. It has a circular permanent magnet with a number of projections or teeth corresponding to the number of engine cylinders, and a stationary coil of fine enameled copper wire wound on a plastic reel and positioned inside the magnet.
stator windings
A winding in an alternator that creates the current output, or a winding in a motor that creates the needed magnetism for the motor to rotate.
stator winding
A winding in an alternator that creates the current output, or a winding in a motor that creates the needed magnetism for the motor to rotate.
steel hammer
A hammer with a head made of hardened steel.
steel rule
An accurate measuring ruler made of steel.
steel-disc–type rim
A plain steel wheel that is typically covered by a hubcap.
steering angle sensor
A sensor that measures the amount of turning a driver desires. This information is used by the ESC system to know the driver’s directional intent.
steering wheel position sensor
A sensor that signals to the EBCM both the position and speed of the steering wheel.
steering knuckles
A device that connects the front wheel to the suspension; pivots on the top and bottom, thus allowing the front wheels to turn.
steering arm
An arm that extends from the steering knuckle. The tie-rods connect to these arms in order to steer the wheels.
steering axis inclination (SAI)
The angle formed by an imaginary line running through the upper and lower steering pivots relative to vertical as viewed from the front.
steering box
A device that converts the rotary motion of the steering wheel to the linear motion needed to steer the vehicle.
steering column
A column affixed between the steering wheel and the steering box, usually made to collapse during a crash.
steering damper
A device used to prevent shocks from irregular roads from being transmitted through the steering linkage and back to the steering wheel.
steering linkage
Steel rods that connect the steering box to the steering arms on the steering knuckle.
steering sensor
A sensor that can read both torque and rotation from the steering wheel.
steering system
A term used to describe all of the components and parts involved in steering a vehicle.
steering knuckle
A device that connects the front wheel to the suspension; pivots on the top and bottom, thus allowing the front wheels to turn.
step-down transformers
A transformer used to reduce the voltage, such as to allow a battery charger operated on 120 volts to charge a 12-volt battery.
step-down transformer
A transformer used to reduce the voltage, such as to allow a battery charger operated on 120 volts to charge a 12-volt battery.
step-up transformer
A transformer used to increase the voltage from a lower input voltage to a higher output, such as an ignition coil.
step-up transformers
A transformer used to increase the voltage from a lower input voltage to a higher output, such as an ignition coil.
stepper motor
A type of brushless motor with a key difference: It is designed to rotate in fixed steps through a set number of degrees.
stepper motor EGR valve
An EGR valve that uses an electrically controlled motor to open the pintle in steps to let exhaust gases flow into the intake manifold.
stoichiometric ratio
The exact ratio between air and fuel, at which both are burned completely. See also lambda.
stop
A rubber part used to control the movement of control arms (suspension arms).
stops
A rubber part used to control the movement of control arms (suspension arms).
straight edges
A measuring device generally made of steel to check how flat a surface is.
straight grinder
A powered grinder with the wheel set at 90 degrees to the shaft.
straight vegetable oil (SVO)
Biodiesel made from plants such as soybeans, jatropha, palms, etc.
straight edge
A measuring device generally made of steel to check how flat a surface is.
strain
An injury caused by the overstretching of muscles and tendons.
stroke
The movement of the piston in the engine from top dead center to bottom dead center, or vice versa. There are four strokes: intake, compression, power, and exhaust.
strut
A shock absorber used on a MacPherson strut–type suspension.
struts
A shock absorber used on a MacPherson strut–type suspension.
stub axle
An axle used for one wheel.
stub-axle carrier
The body of the stub-axle knuckle.
stud
A type of threaded fastener with a thread cut on each end rather than having a bolt head on one end.
subframe
A mount attached to the vehicle that is used to support the engine and transaxle assembly.
suction reed valves
A flat, spring-loaded valve used as a check valve on the suction side of a compressor.
suction reed valve
A flat, spring-loaded valve used as a check valve on the suction side of a compressor.
sulfur
A regulated by-product of petroleum-based (especially diesel) fuel.
sulfur dioxide (SO ₂ )
A pollutant resulting from sulfur in motor fuel and contributing to acid rain.
sulphuric acid
A type of acid that when mixed with pure water forms the basis of battery acid or electrolyte.
sun gear
The center gear of a planetary gear set around which the other gears rotate.
sun load, or solar, sensor
A photodiode that varies voltage based on light. It is used to determine the radiant heat coming from the sun into the passenger cabin and gives an input signal of sunlight load to the ECU.
sun load (solar) sensor
A photodiode that varies voltage based on light. It is used to determine the radiant heat coming from the sun into the passenger cabin and gives an input signal of sunlight load to the ECU.
supercharger
A device that pressurizes airflow into the engine, working similar to a turbocharger. The supercharger is driven by the crankshaft through a belt or gears and does require power from the engine.
superheat spring
A spring used as part of the control in the TXV to ensure refrigerant leaving the evaporator is boiled completely or superheated.
supplemental restraint system (SRS)
A passenger safety system, such as airbags and seat belt pre-tensioners.
supporting statement
A statement that urges the speaker to elaborate on a particular topic.
surface filter
A filter that is a simple screen mechanism to catch dirt and other particles in the hydraulic oil as it passes through.
surface roughness average (Ra)
A measurement used to classify how rough a particular mating surface is at the microscopic level.
surge protector
An electrical protection device for preventing electrical surges.
surge tank
A sealed tank that captures coolant coming from the head that has turned to steam and changes the steam back to coolant to be reused by the cooling system.
suspension action
Movement of the chassis up and down.
suspension strut
A shock absorber designed to reduce spring oscillations.
suspension system
A system within a vehicle designed to isolate the vehicle body from road bumps and vibrations.
swash plate
Another name for an axial plate.
sway bar
A part used in vehicles as a stabilizer, or antiroll bar. It is connected to the chassis in the center, and each end is connected to one side of the suspension system. It is typically installed on the front, and sometimes the rear suspension.
swinging shackle
A shackle connected to the rear of the multileaf spring that allows the leaf spring to move downward when a load is placed on the rear of the vehicle.
switch
An electrical device with contacts that turns current flow on and off.
switching transistor
An electronic device used to control the flow of current through the ignition coil primary winding.
symmetric tread patterns
A tread pattern with the same tread pattern on both sides of the tire; typically nondirectional.
symmetric tread pattern
A tread pattern with the same tread pattern on both sides of the tire; typically nondirectional.
synchromesh transmission
A modern transmission that uses gear synchronizers to match the speeds of gears and shafts during upshifts and downshifts.
synchronizer
An assembly that allows for the selection of gears without grinding by matching the speed of the two assemblies.
synchronizer sleeve
The sleeve that slides to lock the selected gear to the main shaft. The synchronizer sleeve is part of the synchronizer assembly.
syngas
A man-made motor fuel.
synthetic blend
A blend of conventional engine oil and pure synthetic oil.
synthetic oil
Synthetic oil that, in its pure form, uses man-made base stocks and is not derived from crude oil. This oil lasts longer and performs better than normal oil. The base stock additives are similar to those in conventional oils.
Synthetic blends
A blend of conventional engine oil and pure synthetic oil.
T
tandem master cylinders
A master cylinder that has two pistons that operate separate braking circuits so that if a leak develops in one circuit, the other circuit can still operate.
tandem master cylinder
A master cylinder that has two pistons that operate separate braking circuits so that if a leak develops in one circuit, the other circuit can still operate.
tang
A part of the bearing insert that helps to lock the bearing insert into the bearing saddles and caps.
tangs
A part of the bearing insert that helps to lock the bearing insert into the bearing saddles and caps.
tanks
Metal or plastic pieces that line the pipes used to connect the tubes together to allow the coolant to continue to flow.
tap handle
A tool designed to securely hold taps for cutting internal threads.
tap
A term used to generically describe an internal thread-cutting tool.
taper
An object that is smaller in diameter at one end.
taper tap
A tap with a tapper; it is usually the first of three taps used when cutting internal threads.
tapered roller bearing assemblies
A type of wheel bearing with races and rollers that are tapered in such a manner that all of the tapered angles meet at a common point, which allows them to roll freely and yet control thrust.
tapered roller bearing assembly
A type of wheel bearing with races and rollers that are tapered in such a manner that all of the tapered angles meet at a common point, which allows them to roll freely and yet control thrust.
tapered seat
A type of lug nut with a tapered end toward the rim that helps center the wheel on the wheel studs.
tappet
Another name for a valve lifter. Tappets may be flat or have rollers to ride on the cam lobes.
tappets
Another name for a valve lifter. Tappets may be flat or have rollers to ride on the cam lobes.
taps
A term used to generically describe an internal thread-cutting tool.
technical service bulletin (TSB)
Information issued by manufacturers to alert technicians of unexpected problems or changes to repair procedures.
Technical service bulletins (TSBs)
Information issued by manufacturers to alert technicians of unexpected problems or changes to repair procedures.
telematics
Satellite-based, two-way communication with the vehicle’s electronic systems.
telescoping gauge
A gauge that expands and locks to the internal diameter of bores; a caliper or outside micrometer is used to measure its size.
temperature grade
A standardized grading system that indicates the extent to which heat is generated or dissipated by a tire.
tensile strength
A measure of how strong a material is as it is being pulled apart.
terminal
A means of providing a low-resistance connection/termination at the end of a wire.
terminals
A means of providing a low-resistance connection/termination at the end of a wire.
test certificate
A certificate issued when lifting equipment has been checked and deemed safe.
tetrafluoroethane (R-134a)
An inert colorless gas that can be used as a refrigerant. It is stored in light blue containers.
thermal runaway
A cycle during battery charging in which heating lowers resistance, which in turn increases current flow, which in turn further increases heat created. During this cycle, dangerous gases may build up, creating the potential for an explosion or damage through excessive current flow.
thermal cycle switch
A normally closed switch located in the fins of the evaporator that controls the air-conditioning compressor clutch. It is opened and closed by the temperature changes in the evaporator.
thermal expansion valve (TXV) system
A system with a valve designed to sense evaporator outlet temperature and vary the inlet orifice size accordingly.
thermistor
A temperature-controlled variable resistor. As temperature changes, so does resistance.
thermo control (temperature-controlled valve)
A mechanical device that moves with temperature. It is typically used to control the flow of vacuum when the engine is either hot or cold.
thermo-control switch
A temperature-sensitive switch that is mounted into the radiator or into a coolant passage on the engine to control electric fan operation.
thermocouple
A temperature-sensing component that consists of two dissimilar metals that produce voltage proportional to temperature.
thermostat
Located under the thermostat housing, the thermostat regulates the flow of coolant, allowing coolant to flow from the engine to the radiator when the engine is running at its operating temperature.
third-degree burns
Burns that involve white or blackened areas and damage to all skin layers and underlying structures and tissues.
thixotropy
The ability of a semisolid grease to flow when agitated or stressed.
thread file
A type of file that cleans clogged or distorted threads on bolts and studs.
thread pitch
The coarseness or fineness of a thread as measured by either the threads per inch or the distance from the peak of one thread to the next. Metric fasteners are measured in millimeters.
thread repair
A generic term to describe a number of processes that can be used to repair threads.
three-angle grind
A process of grinding the valve openings on the cylinder head so that air can pass through them more smoothly and quickly.
three-quarter floating axle
An axle on which there is only one wheel bearing which bears the weight of the vehicle, but the axle prevents the wheel from tipping inward or outward.
three-way catalytic converters
A converter that changes hydrocarbons, carbon monoxide, and oxides of nitrogen into harmless elements.
three-way catalytic converter
A converter that changes hydrocarbons, carbon monoxide, and oxides of nitrogen into harmless elements.
threshold limit values (TLVs)
The maximum allowable concentration of a given material in the surrounding air.
threshold limit value (TLV)
The maximum allowable concentration of a given material in the surrounding air.
throttle
A device used to produce acceleration by controlling the air/fuel mixture.
throttle body
The housing on an intake manifold that is used to control the amount of filtered air that enters the cylinders.
throttle body injection (TBI)
A fuel injection system that uses one or more fuel injectors mounted above or in the throttle body itself. Also called single-point injection.
throttle position sensor (TPS)
A potentiometer that sends an analog signal to the electronic control unit that corresponds to the position of the throttle valve.
throttle position sensor
A sensor that measures how far the throttle valve is opened.
throttle valve
A type of spool valve that is connected to the throttle on a vehicle. The throttle valve creates a pressure proportional to throttle opening and is used to delay upshifting based on throttle opening.
throttle valve pressure
The pressure created by the throttle valve that is proportional to throttle opening.
throw
The part of the crankshaft that is offset for the connecting rods to mate with; also called connecting rod journal.
throw-out bearing
The part of the clutch release mechanism that imparts clutch pedal force to the rotating pressure plate levers.
throws
The part of the crankshaft that is offset for the connecting rods to mate with; also called connecting rod journal.
thrust angle
The angle formed between the centerline of the rear axle in comparison to the centerline of the vehicle.
thrust bearings
A bearing that separates surfaces that are in rotation with each other and controls forward and backward movement between them. They can be of the bushing style as in an engine main thrust bearing, or a roller bearing as in a torrington bearing in an automatic transmission.
thrust line
The imaginary line drawn through the center of the rear axle.
thrust washers
Flat, washer-shaped bearings that provide a wear surface between two rotating components that are loaded axially.
thrust bearing
A bearing that separates surfaces that are in rotation with each other and controls forward and backward movement between them. They can be of the bushing style as in an engine main thrust bearing, or a roller bearing as in a torrington bearing in an automatic transmission.
thrust-type angular-contact ball bearings
A type of bearing that uses a deep groove in the bearing races where the ball bearings ride; this design is for thrust conditions.
thrust-type angular-contact ball bearing
A type of bearing that uses a deep groove in the bearing races where the ball bearings ride; this design is for thrust conditions.
tie-rod
A steering component that transfers linear motion from the steering box to the steering arms at the front wheels.
tie-rod assembly
The part that fits between the rack and the steering arms and transfers the movement of the rack.
timing chain
A steel chain connecting the crankshaft assembly to the camshaft assembly
timing gears
Gears that synchronize the timed events of rotational engine components like camshafts and fuel injection pumps.
timing gear
A sprocket attached to the crankshaft assembly and the camshaft assembly.
tin snips
Cutting device for sheet metal, works in a similar fashion to scissors.
tire inflation pressure
The level of air in the tire that provides it with load-carrying capacity and affects overall vehicle performance.
tire placard
A metal, vinyl, or paper tag permanently affixed to a vehicle that indicates the appropriate tire size and inflation pressure for the vehicle.
tire pressure gauges
A gauge used to measure the air pressure within a tire.
tire pressure monitoring system (TPMS)
An automatic sensor system in most modern vehicles that alerts drivers of tire pressure problems.
tire valve
The valve through which air is inserted into a tire to inflate it.
tire pressure gauge
A gauge used to measure the air pressure within a tire.
title history
A detailed account of a vehicle’s past.
toe-in
When the front of the wheels, as seen from above, are closer together than the rear of the wheels.
toe-out on turns
The difference in turning angle of the inside tire in comparison to the outside tire. This angle difference allows the tires to roll through the corner rather than the inside tire dragging. Also referred to as Ackermann angle.
toe-out
When the rear of the wheels, as seen from above, are closer together than the front of the wheels.
toe-setting
Setting of the toe-in or toe-out of the tires to the centerline of the vehicle.
tone wheel
The part of the wheel speed sensor that has ribs and valleys used to create an electrical signal inside of the pick-up assembly.
top hat parking brake
A drum brake that is located inside a disc brake rotor in order to act as a parking brake.
top dead center (TDC)
The position of the piston in the cylinder when it is farthest from the crankshaft.
toroidal CVT
A type of CVT that uses moveable rollers in contact with input and output drive discs. The rollers transfer power from one drive disc to the other. Their position determines the effective gear ratio.
torque
The amount of twisting force applied in a turning application, usually measured in foot-pounds or Newton meters (Nm).
torque angle
A method of tightening bolts or nuts based on angles of rotation.
torque assist
Use of an electric motor to supplement the engine’s torque whenever additional torque is needed, allowing for a smaller ICE to be used.
torque converter
A device that is turned by the crankshaft and transmits torque to the input shaft of an automatic transmission.
torque converter clutch (TCC)
A hydraulically operated clutch located inside the torque converter that applies at predetermined conditions and stops torque converter slippage.
torque multiplication
The increase of torque.
torque plate
A 2" (51 mm) thick plate that is bolted where the cylinder head is fastened on the engine block.
torque sensor
A device used to measure the load on the steering wheel.
torque smoothing
A process that uses an electric motor to smooth out engine power pulses when an ICE is operating at low rpm or when the vehicle is using fuel management techniques such as cylinder deactivation.
torque specification
Supplied by manufacturers and describes the amount of twisting force allowable for a fastener or a specification showing the twisting force from an engine crankshaft.
torque steer
A condition in which the vehicle pulls to one side during hard acceleration.
torque wrench
A tool used to measure the rotational or twisting force applied to fasteners.
torque specifications
Supplied by manufacturers and describes the amount of twisting force allowable for a fastener or a specification showing the twisting force from an engine crankshaft.
torque-to-yield
A tightening procedure in which a bolt is designed to be slightly elastic when tightened; the elastic bolt retains an even pressure on the head gasket.
torque-to-yield (TTY) bolts
Bolts that are tightened using the torque-to-yield method.
torsion bar
A cylindrical bar made of spring steel that flexes along its length. The bar is firmly attached at each end to a mating component. The torsion bar allows spring-loaded flexing between those components. Torsion bars are typically used as springs in the suspension system and the control valve in power steering systems.
Torsion bars
A cylindrical bar made of spring steel that flexes along its length. The bar is firmly attached at each end to a mating component. The torsion bar allows spring-loaded flexing between those components. Torsion bars are typically used as springs in the suspension system and the control valve in power steering systems.
torsional load
A force that is applied by clamping one end of an object to another object that is then twisted.
torsional vibrations
The speeding up and slowing down of a shaft, which happen at a relatively high frequency. Crankshafts have torsional vibrations due to the power pulses of the pistons.
town gas
Locally available gas used to power early internal combustion engines.
toxic dust
Any dust that may contain fine particles that could be harmful to humans or the environment.
traction control system (TCS)
A computer-controlled system added to ABS to help prevent loss of traction while the vehicle is accelerating.
traction grade
A standardized grading system that indicates how well a tire will maintain contact with the road surface when wet.
trailing shoes
Brake shoes installed so that they are applied in the opposite direction to the forward rotation of the brake drum; not self-energizing and less efficient at developing braking force.
trailing arm suspension
A type of suspension system that uses upper and lower control arms.
transaxle
A type of transmission typically used in front-wheel drive vehicles in which the transmission also includes the differential and final drive gear.
transfer case
A component that is bolted to the back of the transmission and connects the front and rear axles via the driveshafts.
Transfer cases
A component that is bolted to the back of the transmission and connects the front and rear axles via the driveshafts.
transformer action
The transfer of electrical energy from one coil to another through induction in a transformer.
transistor
A semiconductor device that allows a small current in the base lead to control a larger current through the emitter collector leads.
transmission
An assembly that houses a variety of gear sets that allow the vehicle to be driven at a wider range of speeds and terrain conditions than would be possible without a transmission.
transmission control module (TCM)
An electronic computer that controls transmission function; it may include adaptive learning capabilities for driver preferences.
transmission input shaft
The shaft that brings engine torque into the transmission.
transmission oil temperature (TOT)
A type of variable resistor used inside the transmission to monitor oil temperature.
transmission specialists
A technician who diagnoses, overhauls, and repairs transmissions.
transmission oil temperature (TOT) sensor
A type of variable resistor used inside the transmission to monitor oil temperature.
transmission specialist
A technician who diagnoses, overhauls, and repairs transmissions.
transmission-mounted parking brake
A drum brake that is mounted on the drive shaft just after the transmission to serve as a parking brake.
transverse
The orientation of the engine in which the front of the engine is facing the side of the vehicle.
tread wear grade
The number imprinted on the sidewall of a tire by the manufacturer as required by the National Highway Traffic Safety Administration (NHTSA) that indicates the tread life of a tire’s tread.
triangular file
A type of file with three sides so it can get into internal corners.
triangulation
A method of locating an object using mathematics based on forming a triangle with two known points.
trilateration
A method of locating points by the measurement of distances using geometry.
trim height
The amount of ground clearance a vehicle has, measured from a point on the body or frame depending on the manufacturer. Also known as ride height.
trimetal
The use of three different types of metals to build up a bearing insert to give it long-lasting wear characteristics.
truck
A large heavy vehicle for carrying cargo.
tube flaring tool
A tool that makes a sealing flare on the end of metal tubing.
tubes
Metal pipes running side to side or up and down that the coolant or refrigerant travels through.
tubing cutter
A hand tool for cutting pipe or tubing squarely.
tulip/tripod joint
A constant velocity joint that has three equally spaced fingers shaped like a star. This configuration allows in-and-out movement of the shaft while allowing flexing.
turbocharger
A device that pressurizes airflow into the engine. The turbocharger works similar to a supercharger, but is driven by the exhaust gases.
turn signal switch
A switch that turns the left and right turn signal lights on and off.
turning radius
A measure of how small a circle the vehicle can turn around when the steering wheel is turned to the limit.
twin leading shoe drum brake system
Brake shoe arrangement in which both brake shoes are self-energizing in the forward direction.
twist drill
A hardened steel drill bit for making holes in metals, plastics, and wood.
twisted pair
Two conductors that are twisted together to reduce electrical interference.
two-mode hybrid
A type of hybrid drive system in which there are two distinct modes of operation. In one mode, the electric motor can propel the vehicle and be used for regenerative braking; in the second mode, the electric motors can be used to assist the engine while the engine uses fuel management techniques such as cylinder deactivation.
two-post hoists
A type of vehicle hoist that uses two parts (one on each side of vehicle) and four arms to lift the vehicle.
two-post hoist
A type of vehicle hoist that uses two parts (one on each side of vehicle) and four arms to lift the vehicle.
two-stroke engine
An engine that uses only two strokes to complete its running cycle.
two-stroke
An engine that uses only two strokes to complete its running cycle.
two-way catalytic converter
A converter that changes only hydrocarbons and carbon monoxide into harmless elements.
U
ultrasonic
A method of leak detection that uses a sensitive microphone to hear small refrigerant leaks by amplifying the hissing noise.
umbrella-style valve stem seals
A seal that surrounds the top of the valve stem to prevent excessive oil from leaking into the valve stem.
umbrella-style valve stem seal
A seal that surrounds the top of the valve stem to prevent excessive oil from leaking into the valve stem.
understeer
A condition in which a vehicle’s front wheels turn sharper than the vehicle’s direction when the vehicle is steered around a corner. This vehicle is said to be “loose” in the corners.
unibody construction
A construction style that uses the body sheet metal as the frame of the vehicle. Typically this type of construction uses small frame sections called subframes.
unibody design
A vehicle design that does not use a rigid frame to support the body. The body panels are designed to provide the strength for the vehicle.
uniform pitch
A spring whose pitch (the distance from the center of one coil to the center of the adjacent coil) is the same distance throughout.
Uniform Tire Quality Grading (UTQG)
A standardized grading system established by the National Highway Traffic Safety Administration (NHTSA) designed to provide tire buyers with a comparative measure of a tire’s tread life, traction, and temperature characteristics.
unitized wheel bearing hub
An assembly consisting of the hub, wheel bearing(s), and possibly the wheel flange, which is preassembled and ready to be installed on a vehicle.
universal joints
A cross-shaped joint with bearings on each leg where one set of parallel legs is connected to the end of one shaft and the other set of parallel legs is connected to the end of a second shaft. This arrangement allows the shafts to operate at shallow angles to each other.
universal joint (u-joint)
A cross-shaped joint with bearings on each leg where one set of parallel legs is connected to the end of one shaft and the other set of parallel legs is connected to the end of a second shaft. This arrangement allows the shafts to operate at shallow angles to each other.
unsprung mass
Any part of the steering and suspension system that is not supported by springs. A large amount of unsprung weight will cause the tire to hop off the ground when hitting bumps, as the weight will overcome dampening of the shock absorbers.
unsprung weight
See unsprung mass.
urea
A chemical reactant specifically designed for use in selective catalytic reduction systems to reduce nitrogen oxides. Also called diesel exhaust fluid.
V
V blocks
Metal blocks with a V-shaped cutout for holding shafts while working on them. Also referred to as vee blocks.
V engines
A term used to describe an engine configuration that uses a single bank of cylinders staggered at a shallow 15-degree V.
vacuum bleeding
Bleeding process that uses a vacuum bleeder to pull the air and old brake fluid from the system.
vacuum tube fluorescent (VTF)
A type of lighting used for instrumentation displays on vehicle instrument panel clusters. This type of lighting emits a very bright light with high contrast and can display in various colors. Also called vacuum fluorescent display (VFD).
vacuum
A pressure in an enclosed area that is lower than atmospheric pressure.
vacuum advance unit
A mechanism that controls ignition timing advance in relation to engine load and causes the spark at the spark plug to occur sooner based on engine conditions. Its function is to improve fuel economy and, in doing so, reduce exhaust emissions.
vacuum gauge
A device used to measure the amount of vacuum an engine can generate during various operating conditions.
vacuum modulator
A device on a hydraulically controlled transmission that converts engine manifold vacuum into an engine load signal called modulator pressure.
vacuum pump
A pump used to evacuate the airconditioning system and put it into a deep vacuum or low pressure to remove moisture.
vacuum servos
A vacuum-controlled device that moves the air doors of the air box. It is controlled by the vacuum that comes from the vacuum-type climate control panel.
vacuum relief valve
A mechanical valve used on the gas cap that prevents a low-pressure condition from occurring. It also ensures that the fuel tank will not collapse due to fuel usage or contraction of fuel on cooldown.
vacuum servo
A vacuum-controlled device that moves the air doors of the air box. It is controlled by the vacuum that comes from the vacuum-type climate control panel.
vacuum-relief valve
A mechanical valve used on the gas cap that prevents a low-pressure condition from occurring. It also ensures that the fuel tank will not collapse due to fuel usage or contraction of fuel on cooldown.
validating statement
A statement that shows common interest in the topic being discussed.
valve
A device used to control the flow of air and fuel into the combustion chamber and exhaust gases out of the combustion chamber.
valve body
An aluminum or cast iron housing inside the transmission that houses the majority of the valves that control transmission operation.
valve core
The one-way spring-loaded valve that screws into the valve stem that allows air to be pumped into a tire and prevents it from flowing out.
valve cover gaskets
A gasket used to seal the valve cover (also called a rocker arm cover or cylinder head cover) to the cylinder head assembly.
valve face
A machined surface on the back of the valve head; this area seals onto the valve seat in the cylinder head.
valve float
A condition that occurs when the valves are moving so fast that the spring tension is not great enough to fully seat the valves as designed.
valve guide
An insert in the cylinder head through which the valve stem passes and moves.
valve head
The portion of the valve that is exposed to the combustion chamber and contains the valve face and margin.
valve keepers
A device used to keep the valve spring retainers attached to the valve while in the cylinder head.
valve lifter
A device that transfers motion from the cam lobe to a pushrod or directly acts on the valve and spring, depending on if the cam is in the engine block or the cylinder head; sometimes called a tappet.
valve margin
The flat surface on the outer edge of the valve head between the valve head and the valve face.
valve overlap
The time, usually expressed in degrees of crankshaft rotation, during which both the intake valve and the exhaust valve are open at the same time.
valve seat
An integral part of the head, or circular metal rings that are pressed into the cylinder head, that makes up the mating surface where the valve face sits when it is closed.
valve spring
A metal coil spring that returns valves to their fully closed positions after being opened.
valve spring retainer
A washer-shaped piece of metal positioned near the top of the valve stem that holds the top of the valve spring to keep pressure on the valve while in the cylinder head.
valve stem
The shaft that is attached to the valve head and provides the sliding surface for the valve in its guide as it opens and closes.
valve stem (tire)
A rubber or steel piece that attaches the tire valve to the rim.
valve stem cap
A cap that fits tightly onto the valve stem to prevent debris from clogging it and acts as a secondary seal.
valve tip
The end of the valve stem against which the rocker arm, cam follower, or hydraulic bucket-style lifter directly presses to open the valve.
valve train
A system encompassing all of the parts used in the opening and closing of the valves.
valve seats
An integral part of the head, or circular metal rings that are pressed into the cylinder head, that makes up the mating surface where the valve face sits when it is closed.
Valve guides
An insert in the cylinder head through which the valve stem passes and moves.
valve keeper
A device used to keep the valve spring retainers attached to the valve while in the cylinder head.
valve cover gasket
A gasket used to seal the valve cover (also called a rocker arm cover or cylinder head cover) to the cylinder head assembly.
valves
A means for air to enter and exhaust gases to exit the cylinder.
vane pump
A type of front pump in an automatic transmission that uses small vanes placed radially around a center hub. The vanes may be forced out against the housing of the pump by centrifugal force. The volume between the vanes varies as the pump turns, resulting in fluid being forced out of the pump.
vane-type phaser
A cam phaser that uses vanes inside to allow oil pressure to push against and change cam timing as it is turning.
vapor line
A rubber or plastic line that carries vapors from the fuel tank to the charcoal canister.
vapor lock
A situation in which vapor forms in the fuel line, and the bubbles of vapor block the flow of fuel and stop the engine.
vaporization
The changing of a liquid to a gas through boiling.
variable reluctance sensors
A type of wheel speed sensor that uses the principle of magnetic induction to create its signal.
variable resistors
A component that has a mechanism for varying resistance.
variable displacement vane pump
A type of front pump that uses a vane-style pump that can pivot so that its displacement can be varied.
variable reluctance sensor
A type of wheel speed sensor that uses the principle of magnetic induction to create its signal.
variable voltage signal
A signal that changes based on what the sensor is reading; for example, as temperature varies, so does the voltage signal to the ECU.
variable orifice
A system in which a replaceable, spring-loaded PCV valve regulates gas flow. The position of the PCV valve is controlled by the pressure in the manifold.
variable resistor
A component that has a mechanism for varying resistance.
variable-diameter pulley (VDP)
A type of CVT that uses two pulleys with moveable sheaves, allowing the effective diameter of the pulleys to change, resulting in variable gear ratios.
variable-orifice PVC system
A system in which a replaceable, spring-loaded PCV valve regulates gas flow. The position of the PCV valve is controlled by the pressure in the manifold.
vehicle speed sensors
A sensor used by the PCM to measure vehicle speed. It is often located in the transmission extension housing.
vehicle emission control information (VECI) label
A label used by technicians to identify engine and emission control information for the vehicle.
vehicle hoists
A type of vehicle lifting tool designed to lift the entire vehicle.
vehicle identification number (VIN)
A unique serial number that is assigned to each vehicle produced.
vehicle inspection pits
A trench permanently fitted into the floor of the shop to allow easy work access to the vehicle’s underside.
vehicle jack
A tool for lifting a vehicle.
vehicle safety certification (VSC) label
A label certifying that the vehicle meets the Federal Motor Vehicle Safety, Bumper, and Theft Prevention Standards in effect at the time of manufacture.
vehicle speed sensor (VSS)
A sensor used by the PCM to measure vehicle speed. It is often located in the transmission extension housing.
vehicle hoist
A type of vehicle lifting tool designed to lift the entire vehicle.
vehicle inspection pit
A trench permanently fitted into the floor of the shop to allow easy work access to the vehicle’s underside.
vehicle speed sensor
A sensor used by the PCM to measure vehicle speed. It is often located in the transmission extension housing.
vent solenoid
A solenoid that allows fresh air to enter the evaporative system during a purge event. Also used for an evaporative system monitoring test.
ventilated rotors
A type of brake rotor with passages between the rotor surfaces that are used to improve heat transfer to the atmosphere.
ventilated rotor
A type of brake rotor with passages between the rotor surfaces that are used to improve heat transfer to the atmosphere.
venturi
A restriction (narrowed area) in the air horn.
venturi effect
The reduction in pressure that results when a fluid or air flows through a constricted section of pipe.
vernier caliper
An accurate measuring device for internal, external, and depth measurements that incorporates fixed and adjustable jaws.
vernier calipers
An accurate measuring device for internal, external, and depth measurements that incorporates fixed and adjustable jaws.
VIN
A unique serial number that is assigned to each vehicle produced.
viscosity
The measurement of the thickness of a liquid.
viscosity index improver
An oil additive that resists a change in viscosity over a range of temperatures.
viscosity value
A measurement of resistance to diesel fuel flow.
viscous coupler
Called a fan clutch, a hub that connects the water pump drive to the cooling fan using a temperature-sensitive viscous fluid to cause the fan to turn faster as the temperature of the air pulled through the radiator increases.
viscous coupling
An silicone clutch assembly used in all-wheel drive differentials to provide a slight amount of differential action for control of axle rotational speeds.
volatile organic compounds (VOCs)
The hydrocarbons in petroleum products that contribute to combustion.
volatile organic compound (VOC)
The hydrocarbons in petroleum products that contribute to combustion.
volt
The unit used to measure potential difference or electrical pressure.
voltage
The pressure aspect of electricity, measured to show the potential of a circuit to do work.
voltage drop
The amount of potential difference between two points in a circuit.
voltages
The pressure aspect of electricity, measured to show the potential of a circuit to do work.
volts
The unit used to measure potential difference or electrical pressure.
volumetric efficiency (VE)
A ratio, given as a percentage, of the amount of air actually inducted at a given engine speed at full throttle compared to the internal engine displacement. For a normally aspirated engine (without supercharging or turbocharging), an engine’s volumetric efficiency may peak at around 85%. Peak engine torque is developed at peak volumetric efficiency.
vortex flow
State in which the fluid in the torque converter is traveling between the turbine, stator, and impeller.
W
wad punches
A type of punch that is hollow for cutting circular shapes in soft materials such as gaskets.
wad punch
A type of punch that is hollow for cutting circular shapes in soft materials such as gaskets.
warding file
A type of thin, flat file with a tapered end.
warm-up cycle
One drive cycle, during which the vehicle starts out cold, warms up, and then cools down after the driving cycle.
warpage
A change in the shape of a surface due to distortion or wear.
waste cylinder
The cylinder in a waste spark ignition system that receives a spark near the top of its exhaust stroke.
waste spark system
An ignition system in which each ignition coil serves two cylinders, with each end of the secondary winding attached by a hightension lead to a spark plug. The spark is used to ignite the air–fuel mixture in one cylinder and has no effect on the other cylinder.
waste vegetable oil (WVO)
Used cooking grease or oil used for producing biodiesel fuel.
waste spark ignition system
An ignition system in which each ignition coil serves two cylinders, with each end of the secondary winding attached by a high-tension lead to a spark plug. The spark is used to ignite the air–fuel mixture in one cylinder and has no effect on the other cylinder.
wastegate
A pressure regulator device that allows control of the pressure produced by the turbocharger. The wastegate moves to allow exhaust gases to bypass the turbine wheel of the turbocharger and flow down the exhaust pipe.
water fade
Brake fade caused by water-soaked brake linings.
water gas
A gas made from hydrogen and water.
water jacket
A passageway for coolant to flow inside the engine block that is formed when the block is cast.
water jackets
A passageway for coolant to flow inside the engine block that is formed when the block is cast.
watt
The unit for measuring electrical power.
Watt’s linkage
Another name for a rigid-axle coil spring suspension that uses two bars similar to a panhard rod and a pivot point on the axle to keep the axle from moving in turns.
waveform
A graphical plot of voltage over time that is displayed on an oscilloscope.
web
A reinforced area of a metal part formed during the casting process to create strength and durability.
webs
A reinforced area of a metal part formed during the casting process to create strength and durability.
wedge combustion chamber
A combustion chamber design where the valves are often directly lined up beside each other in a row and positioned at an angle over the pistons, forming a wedge-shaped combustion chamber.
weight transfer
Weight moving from one set of wheels to the other set of wheels during braking, acceleration, or cornering.
weight matching
The process of matching the tire’s lightest point with the rim’s heaviest point (generally at the valve stem) for the purpose of reducing the tire’s radial imbalance.
welch plugs
A soft, round, metal disc pressed into the engine block to plug a water jacket or oil passageway.
welch plug
A soft, round, metal disc pressed into the engine block to plug a water jacket or oil passageway.
welding helmet
Protective gear designed for arc welding; it provides protection against foreign particles entering the eye, and the lens is tinted to reduce the glare of the welding arc.
wet sleeve
A replaceable steel cylinder installed into the block that provides a wear surface for the piston and rings. It is in direct contact with coolant on its outside surface.
wheel cylinder
A hydraulic cylinder with one or two pistons, seals, dust boots, and a bleeder screw that pushes the brake shoes into contact with the brake drum to slow or stop the vehicle.
wheel cylinder piston clamp
A tool that prevents the pistons from being pushed out of the wheel cylinders while the brake shoes are being replaced.
wheel speed sensor
A device that creates an analog or digital signal according to the speed of the wheel.
wheel studs
Threaded fasteners that are pressed into the wheel hub flange and used to bolt the wheel onto the vehicle.
wheel bearings
A component that allows the wheels to rotate freely while supporting the weight of the vehicle, made up of an inner race, outer race, rollers or balls, and a cage.
wheel assembly
A term used to encompass all components of the wheel and tire.
wheel bearing
A component that allows the wheels to rotate freely while supporting the weight of the vehicle, made up of an inner race, outer race, rollers or balls, and a cage.
wheel center
The part of the wheel containing the holes for the lug studs.
wheel retaining nuts
Lug nuts used to hold the wheel on the hub.
wheel rims
The part on which the tire is mounted. Also called a “wheel” or “rim.”
wheel alignment
The practice of aligning the wheels of the vehicle to the centerline of the vehicle and to each other. It ensures that the vehicle will handle correctly and gives best tire wear.
wheel rim
The part on which the tire is mounted. Also called a “wheel” or “rim.”
windage tray
A plate that bolts onto the bottom of the engine between the crankshaft and the oil pan, helping to keep the crankshaft from contacting the engine oil.
wire
A conductor usually made of multistranded copper with an external insulated coating.
wire feed welders
A welding machine that automatically feeds the filler wire by operating a trigger mechanism on a welding gun.
wire feed welder
A welding machine that automatically feeds the filler wire by operating a trigger mechanism on a welding gun.
wiring harness connectors
A plug that contains multiple terminals with male and female ends.
wiring harnesses
A collection of wires or cables insulated from each other but bound together.
wiring diagrams
A schematic drawing and symbol representation of the wiring and components; also called electrical schematic.
wiring diagram
A schematic drawing and symbol representation of the wiring and components; also called electrical schematic.
wiring harness connector
A plug that contains multiple terminals with male and female ends.
wiring harness
A collection of wires or cables insulated from each other but bound together.
wishbone control arm
Another term for an A-arm.
wood gas
A gas made by the carbonization or gasification of coal.
Woodruff key
A half-round, rectangular key that is placed into a half-round, rectangular opening in the nose of the crankshaft or other round shafts found on the engine.
work
The result of force creating movement.
working pressure
The pressure within a hydraulic system while the system is being operated.
worm
A gear with a helical, threaded shaft that is attached to the steering column and meshes with a worm wheel that transfers motion from the steering wheel to the steering linkage.
worm gear steering
A robust steering system frequently used on heavier vehicles that uses a worm to turn a meshed worm wheel to provide gear reduction, making steering easier for the driver.
worm shaft
The protrusion of the worm gear that serves as the point of attachment to the steering column.
wrap leaf
A spring containing spring eyes.
wrenches
A generic term to describe tools that tighten and loosen fasteners with hexagonal heads.
X
XH-7
A form of desiccant used with pure R-134a.
XH-9
A form of desiccant used when the refrigerant may not be pure, such as with some imports.
Y
yaw sensor
A sensor that measures the amount a vehicle is turning around its vertical axis. This information is used by the ESC system to know how much a vehicle is turning.
yaw
Movement of a vehicle around its z-axis (vertical axis) felt when the vehicle deviates from its straight path, as when skidding sideways and the rear comes around.
yield point
The point at which a bolt is stretched so hard that it will not return to its original length when loosened; it is measured in pounds per square inch of bolt cross section.
Z
Zener diode
A diode that forward biases when a certain voltage is reached.
zero camber
A tire with no tilt or zero camber angle.
zero offset
A condition in which the plane of the hub mounting surface is even with the centerline of the wheel.
zero scrub radius
A condition in which the point of center contact between the road surface and the tire and the point where the steering axis centerline contacts the road surface intersect at the road surface.
Zyglo™
A crack detection method used on engine blocks and cylinder heads that uses magnetism and a fluorescent light to find cracks in ferrous metal.