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Automotive Definitions and Definitions for
Auto Parts
A-F
  

Definitions G-L

Definitions M-R

Definitions S-Z

  
Auto Parts Definitions

ABS 
Antilock Braking System (sometimes Antiskid Braking System) Electromechanical system used in vehicles and aircraft to avoid wheel locking during braking.

ABS Pressure Switch
The pressure switch is built inside the ABS unit and signals the ABS control unit to verify there is enough ABS pressure in the system.

AC
Alternating Current: The common form of electricity from power plant to home/office. Its direction is reversed 60 times per second in the U.S.; 50 times in Europe.

Acceleration Sensor
A device, such as a photoelectric cell, that receives and responds to a signal or stimulus and provides acceleration data to computer in electronic shock absorber system.

Accelerator Pump
Device to force a fuel stream into air horn as needed

Accessory Systems
Those that increase comfort or are a convenience for vehicle occupants, such as air conditioning or power windows, and a window defogger.

Accumulator
Air conditioning system component that removes moisture and stores extra refrigerant

AC Generator
Device that produces alternating current; an alternator.

Active Sensor
One that generates its own voltage signal in response to a change in a condition

Active Suspension System
A method of ride control using hydraulic rams, rather than conventional shock absorbers and springs

Actuator Device that performs an action or outputs a signal in response to a signal from a computer.

Adhesive
Substance used to chemically and mechanically bond two materials together

Adjustable Rocker Arm
Used with mechanical lifters; permits changing valve train clearance.

Air Blowgun
Tool used to blow off bits of dirt, solvent, or other debris from parts.

Air Chisel
A cutting tool powered by compressed air that is used to remove faulty exhaust system parts.

Air Cleaner Carbon Element
A canister of carbon granules that absorbs fuel vapors when engine is shut off. 

Air Compressor
A pump that forces air, under pressure, into a storage tank.

Air Cooling system 
The use of cooling fins and air movement to dissipate heat from the engine.

Airflow Sensor
Device to monitor flow of outside air into engine.

Air Horn
Part of the carburetor that channels air into the intake manifold.

Air Injection System
A method of reducing HC and CO emissions by forcing fresh air into the exhaust ports of the engine.

Air Jet Chamber
One that uses an injected stream of air for improved fuel mixing and combustion.

Air Pollution
Release of harmful substances into the air due to engine operation and similar causes.

Air Pump
Belt-driven pump that provides input for the air injection system.

Air Shocks
Shock absorbers that use air pressure, rather than springs, to maintain vehicle height.

Air Spring
Air-filled rubber cylinder that is lighter than the equivalent coil spring.

Air Tests
The use of air pressure to diagnose automatic transmission problems.

Air Tool
A tool powered by compressed air.

ALDL
Assembly line diagnostic link, also called the diagnostic connector.

Alignment Rack
Fixture onto which the vehicle is driven for alignment measurement and adjustment activities.

Alternate Engine
Engine types other than traditional internal combustion, four-stoke-cycle, piston engine.

Alternate Fuel
Fuels other than gasoline and diesel fuel.

Alternator
An AC generator.

Alternator Bearings
Needle or ball-type bearings used 10 provide a low-friction surface for a rotor.

Altitude Compensator
A system that changes the air-fuel ratio as the vehicle moves to higher or lower elevations.

AM
Amplitude modulation (type of radio broadcasting).

Ambient Temperature Switch
One that prevents air conditioner operation when outdoor temperatures are below a set point.

Amplifier
Electronic circuit that uses a small current to control a much larger current.

Amplify
To increase in strength or volume.

Anaerobic Sealer
A sealer that cures in the absence or air.

Analog
A signal that can vary continuously in value.

Analog Signal
One that continually changes strength. Analog voltmeter code Trouble code read by counting the number of needle deflections on a meter.

Antenna Trimmer
Adjustment screw on a radio, used to obtain best reception.

Antifreeze
Liquid used in a cooling system that is mixed with water and prevents the water from freezing. The solution serves as the engine coolant.

Antifreeze Strength
Measurement of concentration of coolant solution.

Antifriction Bearing
Bearing that uses balls or rollers to decrease friction.

Anti-Lock Brake Computer
ECM that accepts wheel sensor inputs and controls braking of the vehicle.

Anti-Lock Brakes
Computer-controlled brakes that will not "lock" and permit wheels to skid.

Anti-Rattle Clips
Metal components designed to keep brake pads from vibrating and rattling.

Anti-Skid System
Another name for anti-lock braking system.

Apprentice Mechanic
A beginner who is learning under direction of an experienced auto technician.

Armature
Rotating support for multiple windings in a motor.

Asbestos
A mineral material once widely used on clutches and brake linings. Asbestos dust is a known cancer-causing agent.

Asbestos Lining
Anti-friction material once widely used for brake linings.

ASE
Abbreviation for National Institute for Automotive Service Excellence, which certifies auto technicians.

Aspect Ratio
The relationship of tire height to width, or profile.

Asphyxiation
Death resulting From lack of oxygen to breathe.

Atmospheric Pressure
The pressure exerted by the Earth's atmosphere (14.7 psi at sea level).

Automatic Clutch Adjuster
A mechanism designed to automatically remove any play from a clutch cable system.

Automatic Temperature Control System
A method of climate control using sensors and a computer to maintain a preset temperature in the vehicle's passenger compartment.

Automatic Transmission
One that does not have to be shifted manually.

Automatic Transmission Electronic Controls
Computerized selection of shift points, based on input from sensors.

Automatic Transmission Fluid
Oil with special additives to make it compatible with Friction clutches arid bands.

Automatic Transmission Slippage
Condition in which engine races as transmission shifts (in severe cases, the car may not move at all).

Automotive Clutch
A mechanical device used to connect and disconnect a manual I transmission from engine power.

Auto Technician's Certification
A program in which technicians take written tests to become certified by the National Institute for Automotive Service Excellence (ASE).

Auxiliary Chain
A chain and sprocket combination used to drive engine auxiliaries, such as the oil pump.

Axle C-clip
Spring steel retainer that fits in a groove on the axle end. 

Axle End Play
In-and-out movement OF the axle, adjusted to specification by using shims.

Axle Retainer Plate
See axle shaft retainer.

Axle Shaft Retainer
Devices that attach to the outside of an axle housing to prevent axles from sliding out. 

Axle Shims
Used between axle housing and retainer to limit end play of the axle.

Backfiring
Condition caused by air-fuel mixture igniting in the intake manifold or exhaust system.

Backing Plate
Component that holds the shoes, wheel cylinder, and other parts inside a drum brake. 

Back Pressure
Pressure developed in the exhaust system when the engine is running.

Backup Light Switch
An electrical switch that completes a circuit to the back up lights whenever the reverse gear if engaged.

Bad Hydraulic Lifter
A cause of valve clatter.

Balancer Shaft
A Rotating component used in some engines to cancel vibration produced by another rotating shaft such as the crankshaft.

Ball and Trunnion U-joint
A seldom-used type of constant velocity U-joint.

Ball Joint
Swivel joint that provides free movement for steering knuckle and control arm.

Ball Joint Balloon Seal
An airtight seal used to protect the ball joint

Ball Joint Wear Indicator
An indicator on the shoulder of the ball joint that shows the amount of wear.

Ball Nut
Component that rides up and down a worm gear as the worm rotates in a recirculating ball gearbox.

Ball Sockets
Components that allow motion in up-and-down and side-to-side direction.

Band
A metal strap with a frictional material lining that can clamp a clutch drum in an automatic transmission to stop its rotation.

Band Adjustment
Check and adjusting the tightness of automatic transmission band for proper automatic transmission shifting and driving conditions.

Bare Cylinder Head
A head with all of its components removed including valves, springs, seals, etc.

Barrel
A cylinder. 

Basic Circuit Problem
One caused by something in the circuit itself that increases or decreases an electrical value.

Battery Activation
To fill with electrolyte then charging a dry battery.

Battery Cables
Heavy gauged wires connected to the battery. Typically two are used. One, connects the battery to the starter (positive) and the second from the battery to a grounding point on the vehicle.

Battery Charge Condition
The state of its plates and electrolyte.

Battery Charger
Device for restoring battery to a proper electrical charge.

Battery Drain Test
A method of checking for unusual current draw with ignition key off.

Battery Leakage Test
Check to determine if current is discharging across top of battery case.

Battery Load Test
A test for battery capacity, made under full electrical load.

Battery Terminal Test
A test for good contact between cables and terminals.

Battery Voltage
For batteries used in modern cars, 12.6V; older cars, 6.3V.

Battery Voltage Test
Check of battery charge with a voltmeter.

BDC
Bottom Dead Center. The lowest position a piston can reach with in its cylinder. 

Bearing Clearance
Small space between moving parts, permitting oil to enter for lubrication.

Bearing Crush
Slight oversize of bearings to jam them in place when cap is tightened on connecting rod. 

Bearing Housing
Section of the turbocharger housing containing the shaft bearings and oil seals. 

Bearing Noise
Constant whir or humming sound due to damage or wear of bearings in the carrier or axle assemblies.

Bearing Packer
Tool used to simplify packing of grease into wheel bearings.

Bearing Spread
Practice of making bearing halves slightly wider than necessary to hold them in place during installation.

Bell Housing
The metal shell surrounding the clutch assembly that bolts to the rear of the engine.

Belted Bias Tire
A bias-ply tire with extra belts added beneath the tread area.

Belts
Fabric made of steel or other material that is placed between body plies and tread.

Belt Squeal
Noise resulting from a slipping drive belt.

Bench Bleed
Method of filling and hand-pumping a master cylinder before installation to remove trapped air.

Bent Push Rod
A cause of valve clatter. Bent rods usually must be replaced.

bhp
Abbreviation for brake horsepower, a measurement of usable horsepower of an engine.

Bias Ply Tire
One with plies running at an angle from bead to bead.

Bleeder Screw
Fitting on top of brake caliper that allows air to be bled from system.

Bleeding
Process of removing any trapped air from a hydraulic system.

Block Diagram
A simple drawing, using rectangles and lines, that shows how sensors, computers, and actuators are interconnected.

Block Heater
A heating device used to warm the block of a diesel engine in cold weather.

Block Line Boring
A technique used to "true" misaligned main bearing bores.

Blow-By
Oil vapors and other emissions that leak past piston rings into the crankcase.

Blower
A fan that forces air to move tough the evaporator of an air conditioning system.

Blow Gun
An air-powered device used for cleaning and drying parts washed in solvent, or blowing away accumulations of dust and dirt.

Blown Head Gasket
Leak of compression from one or more cylinders results from failure of the gasket.

Blow-through Turbo
A turbocharger located ahead of the compressor or throttle body. It compresses only air.

Body Lubrication
Applying oil and grease to such friction points as hinges and latches.

Boiling a Block
Cleaning technique in which strong solvents and heat are used to remove mineral deposits from the water jacket.

Bolt Size
Measurement of the outside thread diameter. 

Boost Pressure
The additional amount of pressure supplied to the intake system produced by a turbocharger or blower.

Boot
Flexible pleated covers placed over the CV joints of a front-wheel-drive vehicle to keep road dirt out of them.

Boot Deterioration
Cracking, tearing, or other damage to a boot, which would allow road dirt and moisture to enter the CV-joint.

Bowl Vent
Passageway that prevents a pressure buildup in fuel bowl.

Box End
A wrench that has completely closed ends that surround and grip a bolt head.

Brake Booster
Component operated by vacuum or power steering system to decrease braking effort needed.

Brake Lines
Metal tubing and rubber hoses connecting master cylinder to wheel brake assemblies.

Brake Pads
Replaceable friction surfaces mounted on caliper of disc brake system.

Brake Pedal Assembly
Foot lever for operating brake system.

Brake Pedal Vibration
Pulsing movement of brake pedal, usually caused by out-of-round brake drum or warped rotor.

Brake Sensor
Provides braking data to computer in electronic shock absorber system.

Brake Shoes
Curved, replaceable friction surfaces used with drum-type brakes.

Brake System
Components that are used to stop a vehicle.

Brake System Flushing
Removal of all old fluid by pressure bleeding, then replacing it with fresh fluid.

Brake Warning Light
Dashboard indicator that warns of low brake system hydraulic pressure. 

Braking Ratio
Comparison of front wheel to rear wheel braking effort.

Break-Away Torque
In a limited-slip differential, the amount of torque needed to make one axle rotate the clutches.

Brushes
Sliding electrical contacts that ride on the slip rings of a generator.

BTU
British thermal units; the units used to measure heat transfer.

Bubbling Sight Glass
A sign that the air conditioning system is low on refrigerant and that air may be present.

Burned Fluid
Condition caused by overheating due to slippage of transmission bands.

Burned Piston
Actual melting or breakage of a part of the piston, resulting in a hole.

Burned Valve
Valve face damaged by heat, allowing leakage of air-fuel mixture from cylinder during compression.

Bus
A pathway for data inside a computer.

Bypass Lubrication System
One that filters only some of the oil going to bearings.

Bypass Valve
Method used to permit coolant circulation in engine when thermostat is closed.

Calibration Fluid
A fluid that is less flammable than diesel fuel, used when testing injectors out of the engine.

Caliper
The component that houses disc brake pads on both sides of the brake rotor and are forced together through applied brake fluid pressure to stop the rotor from turning, thus stopping the car. It is also the name of a tool to measure small inside and outside diameters.

Camber
The inward or outward tilt of a wheel assembly.

Cam Ground Piston
One that is ground slightly out of round to compensate for different rates of expansion.

Cam Lobe Wear
Reduces valve lift, causing reduced engine power and rough idle.

Camshaft
Rotating shaft with lobes that open valves at the correct times for proper engine operation.

Camshaft Drive
Gears, a chain and sprockets, or a belt and sprockets that run the camshaft at half the speed of crankshaft rotation.

Camshaft Lift
Amount of valve train movement produced by the cam lobe.

Cam Thrust Plate
Component that limits front-to-rear movement of camshaft.

Cap Pressure Rating
Pressure at which the cap valve opens to vent coolant to the overflow tube or recovery tank.

Caps
Covers over cell openings on top of a battery.

Carbon Trace
Small line of conductive carbon-like material on a distributor cap or rotor.

Carburetor Cleaner
A chemical used to dissolve gums and material from carburetor parts.

Carburetor Flooding
Excess fuel flow, preventing starting of engine.

Carburetor Fuel System
One that mixes air and fuel and directs it to engine cylinders through an intake manifold.

Carburetor Kit
Gaskets, needle valves, and other parts needed to rebuild a carburetor.

Carburetor Rebuild
Overhaul, with cleaning and part replacement.

Carburetor System
Network of passages that control the air-fuel ratio under specific engine conditions. 

Cartridge Oil Filter
One with a replaceable filter element.

Case
The outer protective shell of a battery, or any other component or device.

Case Bearing Preload
Amount of force pushing differential case bearings together.

Caster
Forward or backward tilt of steering knuckle.

Caster-Camber Bubble Gauge
Instrument with bubbles that indicate degree of tilt.

Catalytic Converter
Device in the exhaust system that oxidizes most harmful emissions from the engine.

Cell
An electrical energy storage device, consisting of negative and positive plates immersed in a conductive fluid (electrolyte).

Cell Voltage Test
Check of individual battery cells for correct charge.

Center Support Bearing
A ball or roller bearing unit that supports the middle of a two-piece drive shaft. 

Centrifugal Advance
A system that uses pivoting weights to advance timing as engine speed increases.

Certified Master Technician
Auto technician who has passed all eight ASE tests.

Certified Technician
Auto technician who has passed at least one ASE test.

Cetane Number
An indication of the cold-starting ability of a diesel fuel.

CFM
Cubic feet of air per minute.

Chain Slap
Flapping motion of chain if slack is permitted.

Charcoal Canister
Unit that traps and stores fuel vapors when engine is not running.

Charge Indicators
Dash-mounted warning light, voltmeter, or ammeter used to show charging system status. Also the visual symbol (often a green dot) that shows state of charge in a battery.

Charging
Current flowing into a battery from an alternator. Also, adding new or recycled refrigerant to an air conditioning or refrigeration system.

Charging Station
Usually, a wheeled cart containing a tank of refrigerant, vacuum pump, and manifold set for adding refrigerant to an air conditioning system.

Charging System
One that uses an alternator to replace the electrical energy drawn from the battery during starting.

Charging System Output Test
A measurement of current and voltage output of the charging system under load.

Charging Voltage
Alternator output that is higher than battery voltage (usually 1 3V- I 5V).

Chassis
The frame and other parts of a vehicle other than the body.

Check Valve
Valve that permits fuel flow in only one direction.

Chemical Burns
Injury to the skin from exposure to toxic or corrosive chemical substances.

Chemical Flushing
Method of removing scale buildup, using a strong chemical and water flush.

CID
Cubic inch displacement.

Circuit Board
A base upon which computer circuits are printed and components are mounted.

Circuit Breaker
Device that interrupts current if a circuit is overloaded or a short occurs. Unlike a fuse, it can be reset.

Circuit Resistance Tests
Measurements of resistance in the insulated and ground circuits of the system.

Clear Sight Glass
A sign that the air conditioning system is operating properly.

Climate Control Computer
ECM that controls temperature levels in the vehicle's passenger compartment.

Clogged Heater Core
One that restricts or blocks flow of coolant, due to an accumulation of rust particles.

Closed Loop
Control system that is constantly changing, based on inputs from sensors.

Closed System
Cooling system using a recovery tank for coolant.

Cloud Point
Temperature at which wax separates out of the fuel.

Cloudy Sight Glass
A sign that desiccant from the receiver-drier is circulating through the air conditioning system.

Clutch
Device that allows the driver to engage or disengage the engine and transmission.

Clutch Adjustment
Process of setting the correct amount of free play in the release mechanism.

Clutch Cable
A simple mechanical arrangement that uses a cable to transmit clutch pedal movement to the clutch fork.

Clutch Chatter
A condition in which clutch severely vibrates as car accelerates.

Clutch Disc
A disc that is splined to transmission input shaft and pressed against the face of the flywheel.

Clutch Fork
Lever that forces the throw-out (release) bearing into pressure plate of clutch.

Clutch Lining
Frictional material riveted to the face of the clutch disk.

Clutch Linkage
A mechanical arrangement of levers and rods that transmits force from the clutch pedal to the clutch fork.

Clutch Master Cylinder
The device that produces the hydraulic pressure needed to operate the clutch.

Clutch Pedal Free Travel
Distance the pedal moves before the throw-out bearing acts on the pressure plate.

Clutch Pilot Shaft
Tool used to keep clutch disc from falling as pressure plate is loosened during clutch disassembly.

Clutch Piston
A piston that moves back and forth inside the clutch drum to clamp driving and driven discs together.

Clutch Release Mechanism
Cable or linkage permitting driver to disengage clutch with foot pedal.

Clutch Slippage
Condition in which engine rpm increases without increase in car's road speed.

Clutch Start Switch
Safety switch that prevents starting motor operation until the clutch is disengaged.

CO
Abbreviation for carbon monoxide, a toxic byproduct of partial burning of fuel.

C02 Readings
Used to evaluate the air-fuel ratio of the engine; measured in percent by volume.

Coast Side
Concave side of gear tooth.

Cogged Belt
Rubber belt with built-in cogs (teeth) that engage the teeth of camshaft and crankshaft sprockets to form a positive drive.

Coil Oscillations
Voltage fluctuations shown on an oscilloscope after the spark plug stops firing.

Coil Spring
Length of spring steel rod wound into a spiral.

Coil Spring Compressor
Tool used to safely compress a spring for removal or installation on a vehicle.

Coil Wire
Conductor carrying high voltage from the coil to the distributor.

Cold Cranking Rating
The amount of current a battery can deliver for 30 seconds at 0~F

Cold Plug
One with a short insulator tip, used in engines operated at high speed.

Cold Soak Cleaner
Cleaning method using unheated solvents to remove oil and grease from disassembled engine parts.

Cold Start Injector
Valve that supplies extra fuel for cold starts.

Combination Valve
One that includes both a suction valve and an expansion valve (used in air conditioning systems). Also braking system valve that can function as a metering or proportioning valve and a brake warning light switch.

Combination Wrench
One that has an open jaw on one end and a box (closed end) on the other.

Combustion Chamber
Area at the top of the cylinder where a spark plug ignites the compressed air-fuel mixture.

Combustion Leak Test
Test that checks for presence of combustion gases in cooling system.

Commutator
Sliding electrical connection between motor windings and brushes.

Commutator End Frame
The end housing on a motor, holding the brushes, brush springs, and shaft bushing.

Compact Spare
Small-diameter spare tire for use in emergencies.

Compression Gauge
Dial indicator used to measure cylinder compression.

Compression Ignition
Ignition of an air-fuel mixture by heat that results from high pressure (compression).

Compression Pressure
The amount of pressure produced in the cylinder by the compression stroke.

Compression Ratio
The relationship of cylinder volumes with the piston at TDC and at BDC.

Compression Ring
Ring that fills the gap between the piston and cylinder wall, preventing blow-by of compression pressure into the crankcase.

Compression Stroke
Piston stroke that compresses the air-fuel mixture in the cylinder.

Compression Test
To check of the compression developed in each engine cylinder and is a means of determining engine condition.

Compressor
Device that pressurizes a refrigerant and forces it through a refrigeration system.

Compressor Assembly
Motor-powered air pump that produces pressure for an electronic height-control system.

Compressor Housing
Outer case around the compressor wheel section of turbocharger.

Compressor Shaft Seal
A common point of refrigerant leakage in a system.

Compressor Wheel
Fan-like wheel that forces air, under pressure, into the engine's intake manifold.

Computer
Electronic device used to control many systems of modern vehicles.

Computer Amplifier
Device that strengthens signals inside the computer.

Computer Analyzer
A more complex testing instrument than a scanner.

Computer Clock
Pacing device that keeps all input, processing, and output operations "in step."

Computer-Coil Ignition
A distributor less ignition system using sensors, a control unit, and multiple ignition coils.

Computer Conditioner
Interface that converts digital signals to analog and vice versa.

Computer Controlled Carburetor
One that calculates and sets air-fuel ratio based on input from sensors.

Computer Harness Connector
Plug at the end of a wiring harness, with one prong for each wire.

Computerized Emission Control System
A computer controlled system that uses sensors, a catalytic converter, and fuel injection to minimize emissions of harmful substances.

Computer Memory
Storage area where data is held electronically.

Computer Menu
The list of tasks or programs initially shown on a computer screen

Computer Scan Values
Output from the vehicle's computer system that can be read by a diagnostic scanner.

Computer Terminal Values
Voltage and resistance values at the ECU connector, read by a digital VOM.

Computer Trouble Codes
Numeric codes, shown on a display or as pulses, that indicate the nature or location of a problem.

Computer Voltage Regulator
Device that provides a very smooth DC voltage for circuits and devices controlled by the computer.

Condensation
Change from a gas to a liquid state.

Condenser
An electrical component in contact point distributors that prevents arcing as points open and close. Also, a device that allows refrigerant to give off absorbed heat and change from a gas back to a liquid state.

Conduction
Method of heat transfer through direct contact.

Conductor
A material that permits easy flow of electrons.

Connecting Rod
Part that fastens the piston to the crankshaft.

Connecting Rod Side Clearance
Distance between side of the connecting rod and the side of the crankshaft journal.

Constant Velocity Joint
One that uses two cross-and-roller joints connected by a centering socket and center yoke.

Contact Pattern
The area of a gear tooth where the matching gear's tooth physically contacts it.

Contact Point Regulator
An older type of voltage regulator that has largely been replaced by the electronic type.

Contact Points
In older distributors, the spring-loaded electrical "make/break" switch contacts.

Continuous Injection
Fuel injection that is constant.

Continuously Variable Transmission
One that has an infinite number of driving ratios and uses belts and pulleys, rather than planetary gear sets.

Control Arm Bushing
Sleeve that allows control arm to swing up and down.

Control Arms
Movable lever arm that forms part of a vehicle's suspension system.

Control Rod
A toothed shaft that rotates control sleeves to control the output of a diesel injector pump.

Control Sleeve
Rotating sleeve around the plunger of a diesel injection pump that helps control pump output.

Convection
A method of heat transfer through air or fluid medium.

Conventional Measuring System
The system of feet, inches, pounds, etc., traditionally used in the United States.

Converter Housing
Case containing the fluid coupling (torque converter) used with an automatic transmission.

Cooling System
Radiator and other components that allow a coolant to circulate and maintain a constant engine operating temperature.

Cooling System Hydrometer
Test instrument used to check specific gravity of coolant.

Cooling System Pressure Test
A method of checking for leaks by placing system under pressure. 

Cooperative Training
Work release program combining school classes with work experience.

CO Readings
When reading CO levels, an exhaust analyzer provides a percentage by volume output.

Cotter Pin
A soft metal pin that fits through hole in a nut and is then spread to lock components in place.

Countershaft
A Shaft on which cluster gears are mounted that transmits force from input gears to output gears.

Countershaft Gear
Cluster of gears in a manual transmission that transmit force from input gears to output gears.

Cradle
Sub-frame supporting the engine of some vehicles.

Crankcase
Lower portion of the block, containing the crankshaft.

Crank Position Sensor
Similar to a distributor pickup coil, the sensor is activated by the teeth on a pulse ring in a crankshaft triggered ignition system.

Crankshaft
Component that changes the up-and-down motion of the pistons into rotating motion. 

Crankshaft End Play
End-to-end movement of crankshaft in block.

Crankshaft Front Oil Seal
Component that keeps oil from leaking between the crankshaft snout and the engine front cover.

Crankshaft Position Sensor
Device to monitor engine speed.

Crankshaft Pulley
Pulley, attached to harmonic balancer, that drives belts for alternator and other units.

Crankshaft Triggered Ignition
System that places trigger wheel and pickup coil on the crankshaft damper at the front of the engine.

Crankshaft Turning
Grinding or otherwise smoothing the surface of crankshaft rod and main journals to repair damage or wear.

Creeper
A low, wheeled cart used to work under a car supported by jackstands.

Crimping Pliers
Special tool used to mechanically fasten connectors to wires.

Crisscross Pattern
Typical pattern used to tighten cylinder head bolts to provide even pressure.

Crossflow
Type of radiator arrangement with tubes running horizontally.

Crossover Pipe
Connector between left and right header pipes in a dual exhaust system, used to equalize backpressure.

Curb Height
Distance from a given point on the car to the ground.

Curb Weight
Weight of vehicle with full gas tank and no passengers or cargo.

Current
The flow of electrons through a conductor.

Cushioning Springs
Flat springs under the friction material on the clutch disc that help smooth the clutch engagement.

CV
Constant velocity.

CV-Joint Repair Kit
Kit containing joint components, replacement boot, grease, and other necessary items for joint repair.

Cybernetics
The study of how electrical-mechanical devices can duplicate actions of the human body.

Cylinder Balance Test
Oscilloscope test that measures the power output from each of the engines cylinders. 

Cylinder Block
Another name for the engine block, or main body of the engine.

Cylinder Bore
Diameter of the engine cylinder.

Cylinder Boring
Machining of cylinder walls to make them perfectly straight and smooth, removing signs of wear and damage.

Cylinder Head
Component that bolts to the top of the engine, enclosing the tops of the cylinders.

Cylinder Head Stand
A fixture used to hold the cylinder head off the workbench surface.

Cylinder Hone
A tool used to develop a pattern of fine scratches on cylinder walls to aid in new ring break-in.

Cylinder Leakage Tester
Instrument used to determine amount of air leakage from combustion chamber.

Cylinder Out-of-Roundness
Condition in which a cylinder diameter is different when measured front-to-back than when measured side-to-side.

Cylinder Sleeving
The practice of inserting a liner into a bored cylinder to restore it to its original diameter.

Cylinder Taper
The slight difference in diameter, due to wear, from the top to the bottom of an engine cylinder.

Cylinder Wear
When the natural up and down movement of the engines piston physically erodes the cylinder walls.

Dash Light Code
The Morse type trouble code conveyed by a flashing light on dashboard.

Dash Warning Light
A labeled indicator that lights to show there is a problem of malfunction.

DC
Direct current.

DC Generator
Device that produces direct current.

Dead Axle
A solid, straight rear axle on a front-wheel-drive vehicle.

Dead Battery
One that has become discharged.

Dead Cylinder
One in which the spark plug is not firing.

Decimal Conversion Chart
Table showing equivalent quantities in fractions of an inch, decimal fractions, and millimeters.

Deck Warpage
Twisting or distortion of engine block surfaces as a result of overhearing.

Delivery Valve
Spring-loaded valves in the outlet fittings to diesel injector pump.

Detonation
Explosive, uneven burning of fuel causing engine knock.

Diagnosis Chart
A listing of problem causes and corrections.

Diagnostic Connector
A terminal to which a diagnostic scanner can be connected to check vehicle operation.

Diagonally Split
Term for a braking system that has each master cylinder piston actuating wheel cylinders that are diagonally opposed.

Diagrams
Drawings that are used to show wiring, vacuum, or hydraulic systems.

Dial Bore Gauge
A tool used to quickly and accurately measure cylinder taper.

Dial Indicator
A device used to measure tiny movements and display the distance on a dial.

Diaphragm Spring Clutch
One that uses a single diaphragm spring, rather than several coil springs, to help release the clutch disk.

Die
Tool for cutting threads on the outside of a rod or shaft.

Diesel Cylinder Balance Test
Diagnostic procedure to determine whether cylinders are firing properly.

Diesel Engine Maintenance
Since diesel engines do not have ignition systems, maintenance (tune-up) work is primarily devoted to making adjustments, changing oil, and replacing filters.

Diesel Fuel Grade
Viscosity rating of a diesel fuel.

Dieseling
Continued engine operation with the ignition turned off (also called "run-on").

Diesel Injection
A mechanical system that forces diesel oil directly into combustion chambers.

Diesel Injection System Tester
Device used to test a number of diesel components and functions by checking pressures.

Diesel Maximum Speed Adjustment
A limitation that can be set by using an adjusting screw on the injection pump.

Diesel Tachometer
Device used to establish the revolutions per minute of a diesel engine.

Differential
An assembly of gears used to provide power to the rear axles and allow them to rotate at different speeds as necessary.

Differential Carrier
Component used to mount the differential assembly on the rear axle housing. 

Differential Case
Case that holds the ring gear, spider gear, and inner ends of the axles.

Differential Lubricant
High viscosity oil used to reduce friction between differential components.

Differential Yoke
Component that connects the rear universal of the drive line to the differential.

Digital Code
Trouble code displayed as actual digits (numbers), rather than flashes.

Digital Display
An oscilloscope that displays a numerical reading (digital display) on a separate screen.

Digital Pyrometer
An electronic device for making accurate temperature measurements.

Digital Signal
One made up of strictly on-off (or high-low) pulses.

Dimmer Switch
A switch that controls high-beam and low-beam headlamp functions.

Diode
Electronic device that allows current flow in only one direction.

Diode Test
Check for open or shorted conditions in a diode, using an ohmmeter or special test equipment.

Dipstick
Strip of stiff metal used to check fluid levels. Markings indicate whether more fluid must be added.

Disc Brakes
Brakes using a caliper that clamps against a rotor for stopping.

Disc Brake Service
Procedure involving worn pad replacement, caliper rebuilding, rotor surfacing, and system bleeding.

Discharging
Flowing out (describing current movement related to a battery).

Disc Resurfacing
Machining the rotor surface to remove wear marks or correct runout.

Disc Runout
Amount of side-to-side movement of brake disc (rotor).

Displacement
The volume displaced by the pistons in moving from BDC to TDC.

Display Output
Actuator that provides readable characters on a small screen or liquid crystal display. 

Distilled Water
Water that has been purified.

Distributor Cap 
A plastic, insulating cover that encloses the distributor rotor and other components.

Distributor Injection Pump
A pump that uses one or two cylinders to handle injection of diesel fuel for an engine, as compared to an inline pump with a plunger for each cylinder.

Distributor Point Gap
Recommended distance between points when fully open.

Distributor Rotor
A slotted shaft on a distributor injector pump that controls fuel flow to each nozzle. 

Distributor Tester
Test device used to check operation of an ignition system distributor.

Distributor Wrench
A specially shaped wrench that allows technician to reach under distributor housing to adjust timing.

Diverter Valve
Component that prevents air from entering the exhaust system during deceleration.

DOHC
Dual Overhead Cam engine.

DOT Number
The Department of Transportation code that indicates the tire has passed required safety rests. It also identifies manufacturer, construction type, and other data.

Double Lap Flare
Approved method of preparing steel fuel lines for connection.

Downflow
Type of radiator arrangement with tubes running vertically.

Dragging Brakes
Braking friction material that remains partially applied, even after the brake pedal is released.

Dragging Clutch
Failure of friction disc to fully disengage from flywheel, even though clutch pedal is depressed.

Draw-Through Turbo
A turbocharger located behind the compressor or throttle body. It compresses the air-fuel mixture.

Drilled Rod
Connecting rod with an oil passage drilled through its length to deliver oil to the piston pin.

Drive Chain
A chain used with some longitudinally mounted engines to transfer power from the engine crankshaft to the transaxle.

Drive Housing
Case surrounding the pinion gear on a starter motor.

Drive Line
The parts that transfer power from the transmission to the drive wheels.

Drivers
Power transistors in a computer that control current flow to actuators.

Drive Shaft
Steel tube that transfers rotating motion from transmission to rear wheels of a car.

Drive Shaft Angle
The angle at which the drive line meets the differential or the transmission.

Drive Shaft Assembly
Components between the transmission and differential, including front and rear yokes, universal joints, and a drive shaft.

Drive Shaft Balance
Equal weight distribution around the axis of the shaft.

Drive Shaft Noise
Sounds typically caused by worn U-joints, worn slip joints, or a faulty center support bearing.

Drive Shaft Runout
Lack of straightness, due to being bent or because of U-joint wear.

Drive Shaft Vibration
A rapid oscillation caused by a shaft imbalance or excessive shaft runout. 

Drive Side
Convex side of gear tooth.

Drive Size
The size of the square opening for the handle of a socket wrench set.

Driving Hub
Mounting for wheel on end of axle. 

Driving Range
Distance a vehicle can be driven without refueling.

Drop Light
An electrical extension cord with a light bulb in a safety cage attached.

Dropping Brake Pedal
Slow descent of brake pedal to floor when brakes are applied. Usually caused by internal leak in master cylinder.

Drum
The housing that holds the parts of a clutch assembly for an automatic transmission. 

Drum Brakes
System that forces brake shoes against the inside of a rotating drum to stop vehicle. 

Drum Brake Service
Process that involves dismounting, disassembling, cleaning, and replacing parts as necessary. Usually, shoes are replaced, wheel cylinders replaced or rebuilt, and the drum is turned (resurfaced). System is then reassembled, bled, and tested.

Drum Grinding
Sometimes done to remove hard spots on a brake drum.

Drum Maximum Diameter
Largest inside diameter allowed for safe operation of drum brakes. 

Drum Resurfacing
Machining of brake drum to remove surface damage.

Dry Charged
Battery that is filled with electrolyte just before being installed in a vehicle.

Dry Park Test
Visual check for looseness of steering components.

Dry Sleeve
A thin cylinder liner that is not exposed to coolant.

Dual Reservoir Master Cylinder
Brake system pump with two pistons and fluid reservoirs for safety.

Dummy Shaft
Tool used to drive out countershaft and reverse idler shaft when disassembling manual transmission.

Dust Cap
Metal cover on end of axle or spindle to keep grease in and road dirt out of bearings.

Dwell
The amount of time distributor points remain closed between openings.

Dwell Meter
One that measures point setting in degrees of distributor rotation.

Dwell Section
Section of oscilloscope pattern used to identify problems in the distributor or electronic control unit.

Dwell Signal
Electronic signal output by carburetor that can be read on a special meter for troubleshooting.

Dwell Variation
Change in meter readings indicating distributor wear.

Dye Penetrate
A testing material that can be sprayed on aluminum or cast iron engine parts to locate cracks. 

Dynamic Imbalance
Tire imbalance that causes both up-and-down and side-to-side movement while rotating.

Dynamometers
Instrument used to measure power output and performance of an engine.

Dyno
An engine dynamometer, used to measure brake horsepower.

ECA
Electronic control assembly; another name for an automotive computer.

ECM
Electronic control module; another name for an automotive computer.

ECU
Electronic control unit; another name for an automotive computer.

Effective Plunger Stroke
The amount of plunger movement that pressurizes fuel in a diesel injector pump.

EFI
Electronic fuel injection.

EFI Self-Diagnosis
The ability of an electronic fuel injection system to display trouble codes.

EFI Tester
A diagnostic device used with EFI systems that do not feature self-diagnosis.

EFI Trouble Code
A digital display or on-off sequence that shows a number code for problem identification.

EGR Valve
Air Gas Re-circulation Valve. A valve allowing exhaust gases to re-enter the intake manifold to be burned again, reducing cylinder temperature and some types of toxic emissions.

Electrical Fire
One that involves, or begins in, electrical wiring.

Electric Engine Fan
One operated by an electric motor, under control of a thermostatic switch.

Electric Fuel Pump
An electrical device that uses a rotary motion to move fuel.

Electrolyte
Liquid that surrounds the plates of a battery and allows a free flow of electrons.

Electronic Advance
A system that uses sensor input and the vehicle's computer to control spark timing. 

Electronic Airbag System
System using impact sensors to deploy an airbag that cushions vehicle operator (and in some cases, passengers) in a collision.

Electronic Coil Module
Grouping of ignition coils and the control unit needed to operate them.

Electronic Control Unit
Another term for a computer used in a vehicle.

Electronic Ignition System
One that uses an electronic control circuit and distributor pickup coil points and condensers to break the field of the ignition coil, sending voltage to the spark plug.

Electronic Ignition Tester
Instrument used to identify source of ignition problems.

Electronic Modules
Small computers in a vehicle, used for specific systems (such as anti-lock brakes or climate control).

Electronic Regulator
Solid-state regulator separate from the alternator.

Electronic Shock Absorber System
One that uses a computer, actuators, and adjustable shock absorbers to regulate stiffness of the vehicle's suspension.

Electronic Steering Assist
Power steering system using an electric motor, rather than hydraulic components.

Electronic Transmission/Transaxle Control System
A computer-based system that controls shift points and torque converter lockup for improved fuel economy.

Element
One of the cells that can be combined to form a battery.

Emergency Brake
Mechanical means of applying rear brakes.

Emission Control System
Components and adjustments used to reduce the amount of pollutants released by operation of an automobile.

Engine
The propulsion system that provides motive power for a vehicle.

Engine Analyzer
Grouping of instruments used to check various engine functions and components. 

Engine Blow-By
Leakage of unburned fuel and other pollutants past piston rings and into the crankcase.

Engine Bottom End
The block, crankshaft, connecting rods, pistons, and related components. 

Engine Break-in
Sequence of acceleration, deceleration, and other operations designed to properly seat and seal new piston rings.

Engine Crane
A portable, wheeled hoist used to lift and remove engines from vehicles.

Engine Efficiency
Ratio of power produced by the engine to the power supplied to that engine. 

Engine Firing Order
The sequence in which spark plugs are fired.

Engine Flooding
Excess fuel in the intake manifold, preventing starting.

Engine Front Cover
Housing of sheet metal or cast aluminum that covers the timing chain or gears.

Engine Front End
A combination of components that operates the camshaft.

Engine Miss
Roughness in engine operation, indicating failure of a spark plug to fire.

Engine Off Self-Test
Test conducted with engine off but ignition key on to cause displaying of trouble codes.

Engine On Self-Test
One conducted with the engine fully warmed up, allowing check of the sensors under normal conditions.

Engine Operating Temperature
Temperature reached by coolant during normal engine operation. 

Engine Overhaul
Process of servicing all internal parts of an engine.

Engine Sensors
Devices that monitor temperatures, fluid levels, and other engine conditions for computer input.

Engine Smoke
Emissions during acceleration or deceleration. Color can indicate engine condition. 

Engine Surge
Rise and fall of engine speed in cruising operation.

Engine Temperature Sensor
Component that measures temperature of engine coolant.

Engine Top End
The cylinder heads, valves, camshaft, and related parts.

Engine Torque
A rating of turning force at the engine crankshaft.

Engine Tune-up
A process of parts replacement and adjustment to return an engine to its peak performance.

EPROM
Erasable programmable read-only memory. 

Erasing Trouble Codes
Removing trouble codes from computer memory after they have been read and the problems corrected.

Ethyl Alcohol
Grain alcohol or ethanol.

Evacuation
A process of removing air and moisture from an emptied air conditioning system, using a vacuum pump.

Evaporator
A device in which refrigerant changes from a liquid to a gas and absorbs heat from its surroundings.

Exhaust Gas Analyzer
Testing device to measure the chemical content of exhaust gases.

Exhaust Gas Sensor
See oxygen sensor.

Exhaust Manifold
Component that directs output of the exhaust ports to the exhaust system.

Exhaust Manifold Heat Valve
A component that forces hot exhaust gases to circulate through intake manifold as an aid to cold-weather starting.

Exhaust Stroke
Piston stroke that forces byproducts of combustion out of the cylinder.

Exhaust System
Components that quiet engine operation and direct combustion products (exhaust gases) to the rear of the vehicle.

Expander-Spacer
Metal ring used with two rails to form oil control ring.

Expansion Plug
Freeze plug designed for installation in tight quarters.

Expansion Tube
A device with a small orifice that meters refrigerant into the evaporator of an air conditioning system.

Expansion Valve
Temperature-sensitive valve that controls refrigerant flow and air conditioner evaporator temperature.

Extension Housing
A separate housing bolted to the transmission housing, containing the output shaft and rear oil seal.

External Oil Leakage
Escape of oil from the engine, usually around gaskets or seals.

Face
Area of a gear tooth above the pitch line. 

Fast Charge(r):
A charger or charge that provides a high current flow for quickly recharging a battery.

Fastener
Devices that hold parts together.

Fast Flushing
Flushing system through a heater hose fitting, without removing the thermostat. 

Fast Idle Cam
A cam that increases idle speed when the choke is closed.

Fast Idle Solenoid
Device that holds throttle plates open when engine is operating, but lets them almost close when engine is shut off.

Feathered Edge
One side of each tread rib is worn sharp and raised; the other side is rounded or recessed.

Feeler Gauge
A thin metal strip or wire of identified thickness, used to measure clearance.

Fender Cover
Cloth or plastic blankets placed over auto body sections to protect the finish while repairs go on.

fhp
Frictional horsepower.

Field Frame
Housing on a motor that holds the field coils.

Field Windings
Stationary windings in a motor that creates a magnetic field to keep the armature rotating. 

Filler Neck Restriction
Metal piece preventing introduction of the larger fuel nozzle used for leaded fuel. 

Fill Ring
Electrolyte level indicator in older style batteries.

Firing Line
The tall spike shown on an oscilloscope, representing the voltage needed to make the spark jump the plug gap.

Firing Order
Sequence in which the spark plugs fire in cylinders.

Fixed Caliper
Brake caliper rigidly mounted to steering knuckle.

Flank
Area on a gear tooth below the pitch line.

Flex Fan
One with blades that alter airflow with engine speed.

Float
Device that rises and falls with fuel level in bowl, opening and closing the needle valve.

Floating Caliper
Brake caliper mounted on t\VO rubber bushings, allowing some movement.

Fluid Contamination
Inclusion of foreign matter in transmission fluid.

Fluid Coupling Fan Clutch
Clutch designed to slip at higher fan speeds.

Fluid Varnish
Sticky, glue-like substance resulting from breakdown of automatic transmission fluid.

Flywheel
Large, heavy wheel mounted on the rear end of the crankshaft. Usually includes a ring gear that is engaged by the starter pinion.

FM
Frequency modulation (type of radio broadcasting).

Force
A pushing or pulling action.

Forward Bias
Arrangement in which diode acts as a conductor.

Four-Gas Analyzer
Measuring instrument that provides the reading of oxygen and carbon dioxide, as well as HC and CO, levels in exhaust.

Four-Stroke Cycle
An engine that takes four piston movements (intake, compression, power, exhaust) to complete a cycle.

Frame
The strong steel structure that supports the body of a vehicle.

Friction Bearing
A Plain bearing with two smooth surfaces sliding on each other. Not a tapered bearing with an outside cone used as the race or riding surface.

Front Cover Gasket
Thin sealing component that is compressed between the cover and the engine.

Front Drive Axles
Shafts that transfer power from the transaxle differential to the vehicle's wheels. 

Front End Rack
Alignment stand.

Fuel Accumulator
Diaphragm that dampens pressure pulses in a fuel injection system.

Fuel Distributor
Hydraulically operated valve used to control fuel flow in a continuous injector system.

Fuel Evaporization System
A combination of technologies and components that prevents fuel vapors from entering the atmosphere.

Fuel Heater
A device used to warm diesel fuel and keep it from jelling into a semi-solid during cold weather. 

Fuel Injection System
General term for systems used with either gasoline or diesel fuel.

Fuel Injector
Fuel valve controlled by a coil or solenoid.

Fuel Pressure Regulator
System that controls pressure of fuel entering injector valves.

Fuel Pump Pressure
The pressure of a fuel pump's output.

Fuel Pump Vacuum
The amount of "pull" exerted on fuel by the pump.

Fuel Pump Volume
The amount of fuel discharged by a pump in a measured period.

Fuel Rail
Tubing that connects several injectors to the main fuel line.

Fuel Return System
One that keeps cool fuel circulating to prevent vapor lock.

Fuel Tank Capacity
How much fuel a tank can hold. 

Full-Floating Piston Pin
One that is free to rotate. It is secured in place with snap rings.

Full Flow Lubrication System
One that forces all oil through a filter before it reaches the parts to be lubricated.

Fully Synchronized Transmission
One in which all forward gears are equipped with synchronizers to allow downshifting while in motion.

Fuse
Device that interrupts current if a circuit is overloaded or a short occurs.

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