Automotive Glossary

  • By Lea Naiz
  • 28 Jun, 2017

Glossary Of Terms Related to Automotive Repair


This acronym denotes “Anti-lock Brake System”.

Air Bag

An inflatable occupant protection device deployed when a motor vehicle experiences sudden deceleration forces.

Air Conditioning Compressor (A/C Compressor)

A device in your vehicle that places a gaseous substance called refrigerant under pressure. Your refrigerator has a compressor and system that works just like the one in your vehicle.

Air Conditioning Condenser

(See “Condenser”)

Air Filtration

Air filters are used to remove abrasive particulate matter from air. Engines breathe massive amounts of air therefore would be damaged if the air was laden with abrasive dust. Many vehicles are using air filtration for the passenger cabin. These filters can also remove allergens.

Air Pump

A device used to pump air into the exhaust system. The additional air is used by the catalytic converter.


A process of aiming, truing and synchronizing the direction that the tires are pointing on a motor vehicle.


A device responsible for recharging the battery. A major component in the vehicles charging system.


(See “Coolant”)

Anti-lock Brake System

A computer controlled braking system intended to prevent any one wheel or combination of wheels from locking up (skidding). Wheels that continue to roll can be steered where as a skidding wheel travels in a straight line. Impact evasion is the goal.

APPS (Accelerator Pedal Position Sensor)

This acronym is used mostly in the Diesel engine world. (See “TPS”)


Advanced technology-partial zero emission vehicle. An emissions standard that meets PZEV requirements and has additional zero-emissions characteristics, such as operation by natural gas or hybrid vehicle batteries.


An acronym denoting “All Wheel Drive”.


A device that delivers rotational torque to the driving wheels on a motor vehicle. Commonly referred to as a “CV axle” or “Axle shaft” or “Half shaft” or “Drive axle”.

Axel Shaft

(See “Axel”) The main difference between an axle and axel shaft that an axel shaft is used in a solid axle housing assemble – known as a “live axle”. Trucks commonly use live axle arrangements. Live axle designs are not considered to be “Independent suspension systems”.

Ball Joint

Movable joints in the steering linkage and suspension system of a vehicle that permit rotating movement in any direction between the parts that are joined – similar to the elbow or knee joint in the human body.

Brake Booster

A device that amplifies the pressure you apply to the brake pedal resulting in increased stopping power. Also reduces driver fatigue.

Brake Caliper

A C-shaped hydro-mechanical device that applies pressure to brake pads when you apply the brake pedal. Compare to your hand when you pick up a dinner plate.

Brake Drum

A shallow bucket-shaped device that rotates with the wheels. Brake shoes ride on the inner surface of the drum. The brake shoes move outward when you apply the brake pedal.

Brake Master Cylinder

A hydraulic pump connected to the brake pedal that moves brake fluid through the brake lines (pipes) to apply the vehicles brakes. (See “Brake Rotor”)

Brake Pads (Brake Shoes or Linings)

Friction material that slides on the brake rotor/drum when you apply the brake pedal. This is the most common “wear” item in the brake system.

Brake Rotor (Disc)

A disc-shaped device that rotates with the wheels. Brake pads ride on the outer surface of the brake rotor. Brake pads literally squeeze the brake rotor when the brakes are applied. (See “Brake Master Cylinder”)

Brake System

A series of components working in harmony to slow a motor vehicle when the brake pedal is applied. (Brake lights, ABS, Brake pads, Brake pedal, Brake master cylinder, etc.)

Carbon Footprint

A measure of the vehicles total consumption of natural resources weighted against the recyclability at EOL (End Of Life)
Carbon Monoxide

One of the harmful components in exhaust gases. Considered a “Greenhouse” gas.

Catalytic Converter

An emission control device located in the exhaust system. The task of the catalytic converter is to chemically convert harmful components of automotive exhaust gases to tolerable levels. The “Cat” is not a filter in any way.

Center Link

A steering component used to move the steering wheels on a motor vehicle left and right. (Picture yourself holding a bar-bell while moving it left and right)

Charging System

The system responsible for recharging the battery in your vehicle.

Check Engine Light

A warning light intended to alert the driver of potential trouble related to vehicle power train components. Concerns that need attention as soon as is reasonably practicable will cause the “Check Engine Light” to come on for as long as the problem persists. Concerns that are considered “damaging” will cause the “Check Engine Light” to flash for as long at the problem persists.

Clock Spring

Refers to a flexible cable related to the driver’s side air bag and is wound like an old clock spring – thus the name. The “Clock Spring” allows the steering wheel to be rotated while still maintaining a reliable connection to the vehicle electronics.


Computer (ECM, PCM, Controller, Electronic Module and many more names)

An Electronic microprocessor based device responsible for receiving inputs through sensory devices, processing data and ultimately controlling engine and vehicle functions.

Condenser (AC)

The component in Air Conditioning systems that cools the refrigerant causing it to change states (Condense) from a gas to a liquid.

Control Arm


As it applies to automotive this term refers to a mechanical system that is cylindrical in shape within the engine block. Pistons travel within the cylinders moving air and fuel mixture in, compressing the A/F mixture, transmitting power to the engines crankshaft and finally moving the spent exhaust gases from the cylinders. Cylinders are sealed chambers where the engines power is generated through the burning of fuel.


Refers to an anti-freeze/ water mixture used to move heat generated by the burning of fuel in the engines cylinders to the radiator and the heater core. Engine coolant is a medium.

CV Joint Boot

A rubber bellows-shaped seal that keeps dirt out of the CV joint and lubricating grease in the CV joint.

CV Joint

This is a common acronym used to denote a Constant Velocity Joint. A CV joint is a device used to deliver rotational torque while operating at an angle. CV joints are used in the front and rear driving axles as well as the drive shaft.

CVT Transmission (Continuously Variable Transmission)

A type of transmission capable of infinite gear ratios – no shifting of gears is required. The goal is efficiency due to a more constant speed of the engine. An engine that can run at a constant speed becomes more efficient with regard to fuel consumption and exhaust emissions.


Any method used to control or limit oscillations of bodies in motion. A shock absorber is used to control vehicle suspension oscillations. When jumping on a trampoline you can use your leg muscles to control or damp the spring motion or energy to control how high you jump.

Diagnostic Procedure

A procedure used to identify root causes of automotive problems. Involves the use of tools and partial disassembly. Diagnosic procedures produce conclusions and are intended to be accurate. We all pay medical doctors for diagnostic procedures due to the complexity of the human systems – the process is similar when applied to automotive due to the ever increasing complexity of vehicles.


A conclusion, decision or end result of a diagnostic procedure. Decisions are made based upon diagnostic conclusions.

Diesel Fuel

As compared to Gasoline Diesel fuel is more viscous, more oil-like, less volatile, possesses more lubricating qualities and contains more energy per gallon.

Diesel Emission Fluid (Urea)

An organic chemical compound used by the Diesel emission control system. Urea is injected into the Diesel exhaust system with the goal of reducing Oxides of Nitrogen (NOx).

Diesel Catalytic Converter

(See “Catalytic Converter”)

Diesel Particulate Filter

As its name implies this device is a filter. Its task is to remove particulate matter from Diesel exhaust gases.


A device that delivers driving forces to axles while at the same time allowing the left and right wheels to rotate at different speeds. When pushing a shopping cart you can make turns because the left and the right wheels are independent of each other. In a motor vehicle the driving wheels are not independent of each other because they have driving axles attached to them therefore when making turns the “Differential” comes into play because the wheel on the inside of the turn is taking a shorter radius / shorter distance than is the outside wheel.

Direct Shift Gearbox (DSG) (Transmission)

Also known as “SMG” or sequential manual gearbox. A type of manual transmission that behaves much like an automatic transmission.

Disc Brakes

A type of brake system commonly used on motor vehicles using brake pads instead of brake shoes. Disc-type brakes use inward pressure (a clamping action) of the friction material to slow the rotational energy of the brake rotor. Generally speaking disc-type brakes have replaced drum-type brakes because of their effective heat-loss character. (See “Brake rotor”)

Drum Brakes

A type of brake system utilizing outward pressure of the friction material (Shoes) and still in use (as of this writing 2014) but on a much smaller scale that in the past. Drum-type brakes have greater holding power than do disc-type brakes but have a tendency to over-heat during operation.

Drag Link

A rod-like steering system component used to deliver the left / right motion of the steering wheel to the steering arms. Sometimes called a “Relay rod”.

Drive Belt

A flexible belt used to operate (drive) power accessories such as power steering and water pump.

Drive Shaft (Prop Shaft / Propeller Shaft)

A rotating shaft delivering power or torque to a drive unit such as a drive axle or differential.

Drivetrain (Powertrain)

A term referring to all components in a vehicle related to propelling the vehicle down the road.

Drive Unit

Refers to device such as a transmission, transfer case or drive axle that delivers torque to something else – even it is the wheels.

Emission Control System

A conglomeration of fully integrated components designed to control / reduce exhaust emissions from motor vehicles.

EGR Valve

An emission control device intended to reduce NOX emissions. The EGR valve re-introduces exhaust gases into the cylinders displacing oxygen causing combustion temperatures to fall ultimately reducing Oxides of Nitrogen production.


Generally refers to electrical wiring, switches, incandescent light bulbs and the like. Generally older technologies related to electricity. It is import to make the distinction between “Electrical” and “Electronics”.

Electronic / Electronics

Generally refers to high-tech solid-state technologies (computers, software, printed circuit boards, fiber optics and the like).

Electronic Throttle Body (ETB)

Commonly known as “Drive by wire” throttle control. This device replaced mechanical throttle controls that were used on older engines. Electronic Throttle Control is a computer-driven method of opening and closing the throttle blade on gasoline internal combustion engines. The advent of this electronic system greatly facilitates vehicle stability systems such as TRACS and ABS as well as cruise control.

Engine Management

This term refers to that portion of the computer system in your vehicle responsible for electronically managing engine functions.

Engine Performance Maintenance (Tune Up)

(Also see “Tune Up”) Refers to care and replacement of “wear” items related to keeping an engine running properly. Spark plugs, fuel filter and induction system service are part of the up-keep.


Ethyl alcohol – used a fuel for the internal combustion engine.

EVAP System

A series of components intended to collect gasoline vapors and reintroduce those vapors to the engine. The gas cap is one part of the EVAP system. Fuel vapors are considered to be air pollution.


Fuel consisting of a mixture of gasoline and up to 85% denatured ethanol.


A petroleum-based organic fuel that is highly flammable (volatile) and produces a great deal of energy when burned with and internal combustion engine.

Flex Fuel Engine

An engine that can be run on more than one type of fuel. (E-85 or gasoline or a mixture)


Motor vehicles depend on many very different lubricating, cooling and hydraulic fluids. (Fuel, Engine oil, Transmission fluid, Engine coolant, Brake fluid, Gear oil, Windshield washer fluid, etc.

Fluid Service

All fluids deteriorate due to age and heat cycles both of which cause some sort of oxidation or chemical activity to take place – usually over time. Fluid service is still a very important “preventive” step that each and every vehicle owner should pay close attention to. The discussion of fluid service intervals has become somewhat controversial at times due to varying opinions of “when” or “if” certain fluids should be changed. Ask your Colchin crew for advice.

Fuel Injector

A electronically controlled spray nozzle responsible for delivering fuel to each cylinder in an engine.

Fuel Injection

This term refers to an entire system responsible for delivering fuel to each cylinder. (See “Engine Management”)

Fuel Pump

Any device (electric or mechanical) used to transfer fuel from the fuel tank to the engine. Fuel pumps also pressurize fuel in preparation for the injection process. (See “Fuel injector”).

Head Unit

Refers to the control / display portion of a vehicle sound system and the HVAC system.

Heat Shield

A device designed to minimize heat transfer from one component to another – usually surrounds exhaust components.

Heater Core

A small heater exchanger located in the interior of the vehicle. Hot engine coolant circulates through the heater core while the blower fan circulates air across the core picking up heat. The heated air is delivered to the interior of the vehicle for occupant comfort and windshield de-icing.


Refers to the Heating / Ventilation / Air Conditioning system.

Independent Suspension

A type of vehicle suspension system that moves up and down on bumps without drastic effect to the other wheels. (See “Live axle”)

Idler Arm

A steering component that mimics the left / right motion of the pitman arm. Also tracks or controls the left / right motion of the center link. (see “Pitman arm” and “Center ling”)

Idler Pulley

A pulley used to guide or stabilize a drive belt.

Induction System Service

A process of cleaning carbon deposits from the internal duct system in an engine know as the “Induction System”. The goal is better MPG and performance. Carbon and tar-like material is a fall-out of fuels and EGR (See EGR System)


A process of visually looking at a part, system or entire vehicle with the goal of compiling information as to its condition. Decisions can be made based upon inspection information. Inspections are usually visual in nature – not to involve tools or disassembly.

Knuckle (Steering)

A steering and suspension system component whose purpose is to track the up and down motion as well as the left / right turning motion of the wheels. Steering knuckles can be used on the front and rear and on both independent and live-axle suspension types.

Leak / Seep (referencing fluids)

A fluid “leak” will in most cases leave evidence (spots) on the garage floor conversely a “seep” will not. This is an important distinction to make when evaluating fluid leaks on motor vehicle systems because decisions can be made as to the severity of the leak and then a decision to “fix or not to fix”.


Acronym for “Low Emission Vehicle”.

Live Axle

A driving axle commonly used on trucks. Used to be used on older cars. Live axles are strong but are heavy and the non-independent nature of them causes suspension system compromises. Independent suspension systems and CV axles have replaced live axles on cars and SUVs.


The act of servicing or making changes to a vehicle which has not failed. Maintenance is considered preventive care. Compare to a fitness program for the human body.


Acronym for “Original Equipment Manufacturer.
Oxygen Sensor

An input sensor to the engine control computer. Gives the computer feedback on fuel mixture calculations. Affects fuel mileage, performance and emissions.

PCV System / PCV Valve

Acronym for “Positive Crankcase Ventilation”. The PCV valve and its related system are one of the first emission controls to show up on motor vehicles in the late 1950s. The PCV system scavenges harmful gases from the engine’s crank case and burns those gases in the cylinders.

Pilot Bearing
A bearing related to the clutch in a manual transmission-equipped vehicle. The Pilot Bearing supports the transmission input shaft and is normally replaced during routine clutch replacement. It is important to note that not all transmission designs use a pilot bearing.

Pitman Arm

A steering component directly connected to the steering shaft (Steering wheel). Place your elbow on your knee and move your hand left and right to see how this device works.


A mechanical reciprocating device that travels in a cylinder compressing and moving gases into and out of the cylinder. Compare to your lower leg as it moves up and down while pedaling a bicycle.


Refers to a portion of the intake manifold system on an engine that delivers air to the engine.

Power Steering

A system of boosting or assisting steering systems and greatly reduces the required force a driver exerts while turning the steering wheel. It is important to note that power steering has been a hydraulic system since it was introduced in the 1950s. Somewhere around 2003 electric power steering began to replace hydraulic systems.

PPS (Pedal Position Sensor)

This acronym is used mostly in the Diesel engine world (See “TPS”).


A rotating drive or driven device used with drive belts.


Partially Zero Emission Vehicle.


A heat exchanger designed to have engine coolant circulated through it while air flows across causing heat to be transferred from away from the vehicle. Cools the engine.

Radius Rod / Arm

A suspension component used to control cornering and braking forces.


The chemical in the Air Conditioning system that makes it cool. Refrigerant is a chemical compound possessing very special properties allowing it to be compressed, change from a gas to a liquid when cooled and absorb heat energy. Refrigerant “relocates” the hot air from inside your vehicle to the outside.

Relay Rod

A steering and/or suspension component used to “relay” input forces to another component.


The act of making changes or corrections to a vehicle component or system which has failed. Compare to a knee surgery.

SCR (Selective Catalytic Reduction)

A process of reducing Oxides of Nitrogen (NOx) in Diesel Exhaust. (See Diesel Emission Fluid).

Seat Belt Retractor

The mechanism that moves your seat belt out of the way when you un-buckle.

Seat Belt Receiver

The part of the seat belt system that you push the metal buckle into.


A device that generates a signal used as an input to the vehicle computer system. Compare to the sensory system in the human body.

Serpentine Belt

A drive belt responsible for spinning power accessories on the engine such as the alternator and water pump. Its name derives from the way this type of belt is wrapped around the drive pulleys – it serpentines around.

Shift Interlock

A safety device designed to prevent inadvertent movement of the shift lever from “Park”. The ignition must be in the on position and the brake pedal applied prior to attempting to move the shift lever from “Park”. Older vehicles were not equipped with this system and there were events where children or dogs left in the vehicle knocked the shifter from “Park” and the vehicle consequently became errant causing bodily injury and property damage.

Shift Linkage / Cable

This mechanism moves other devices inside the transmission causing gear changes (shifting) to take place.

Shock Absorber

A linear device responsible for motion damping / control. A shock absorber allows vehicle suspension to move while preventing it from bouncing uncontrolled. (See “Damping”).


A rotating-toothed drive or driven device used with Timing Belts and drive chains.

Strut (Macpherson Strut)

The term “Strut” is a shortened word used to describe a type of shock absorber widely used in road vehicles. It differs from a true shock absorber in that a strut constitutes / controls the upper section of the suspension.

Sway Bay (Anit-Roll Bar)

A suspension component used to control vehicle body roll resulting from cornering forces. This device causes the vehicle to be more stable during evasive steering maneuvers.


Acronym for “Supplemental Restraint System” – otherwise known as air bag system.


Super-Ultra Low Emission Vehicle.


Acronym for “Traction Control System”

Tie Rod

A steering component that links the left / right steering motion to the left and right front wheels. A tie rod is connected to a steering arm which is part of the knuckle. (See Knuckle)

Tie Rod End

(See “Tie Rod”)


There are many types of thermostats. The one we are describing here is designed to regulate engine operating temperature. It does so by limiting the amount of coolant that gets released to the radiator. All types of thermostats are temperature regulating devices.

Timing Belt

A toothed flexible belt responsible for driving or rotating the cam shaft(s) and in some cases the water pump and oil pump. Similar in function to a bicycle chain.

Timing Belt Tensioner

A device intended to apply proper tension to the Timing Belt. A failed timing belt tension can cause the belt to skip or fall off – similar to a loose bicycle chain.

TPS (Throttle Position Sensor)

An electronic input sensor that gives the vehicle computer system information about throttle angle. Simply put this device tells the computer what you are doing with the gas pedal. (Also see “APPS” or “PPS)

Track Bar

A suspension device whose purpose is to locate and retain the vehicle body over top of its live axle.

Trailing Arm

A suspension device that locates and controls wheel movement / motion.

Transfer Case

A power-transmission device responsible for delivering torque to either the front or rear driving wheels. Commonly used with AWD and 4WD vehicles.


A drive unit responsible for delivering the engine’s torque to the driving wheels. In addition a transmission provides many gear ratios from low-speed to high-speed. Compare to the gears on a mountain bike.


A drive unit with the transmission and differential integrated into one. (See”Differential” and “Transmission”)


An exhaust-driven air compressor. All internal combustion engines breathe air. Turbochargers assist the breathing process by giving an engine pressurized air making it easier for them to breathe. Turbochargers increase an engine’s efficiency because they recover some of the lost heat energy from the exhaust gases.

Tune Up (Engine Performance Maintenance)

This an old term still in use today and it references the maintenance needed to keep engines running properly. The term goes back to the days when we actually did some “Tuning” when making engines run better. Today engines don’t require “Tuning” they require a few wear items to be replaced such as spark plugs and maybe a fuel filter – if equipped. Also Induction system cleaning is a fruitful endeavor (see “Engine Performance Maintenance” and “Induction System Service”).


Ultra Low Emission Vehicle.


There are many valves related to a motor vehicle. This definition applies to the valves in an internal combustion engine. Valves are a reciprocating device that open and close on a precise cycle allowing the ingress air and fuel into the cylinders as well as the egress of spent exhaust gases.


A drive belt used to operate power accessories on the engine such as power steering. Its name comes from its shape.


Vehicle Identification Number. A unique number denoting specific information about each vehicle.

Water Pump

A device that moves engine coolant through passages and the radiator. Automotive water pumps are centrifugal by design. They use an impeller that spins causing the coolant to be thrown to the outside which causes the coolant to move through the engine.

Water Pump Weep Hole

A drain passage for engine coolant to pass externally from a water pump seal when the seal is failing.


An acronym denoting “Four Wheel Drive / 4 Wheel Drive”.


Zero Emission Vehicle.

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