Chapter 1

Glossary of Car Terms


ABS: Anti-lock Brake System

A safety system designed to regulate braking pressure to avoid a skid.


Inflatable safety cushions designed to keep vehicle occupants from impacting interior car surfaces during a collision. Include Front, Side, Knee, and Curtain each defined by which impact direction is protected or which area of the passenger compartment is covered. Curtain airbags inflate down from the roof.

Air conditioning

A climate control system that uses vapor heat-exchange to cool cabin air. Consists of a condenser, compressor, and evaporator along with filters and coolant fluids. System is typically driven by an accessory drive belt.

Air filter

A fiber or paper filter that cleans particulates out of the intake air stream prior to the intake manifold. Filter should be changed at the manufacturer's recommended interval.

Air pollution score

A rating used to compare the amount of smog-producing gasses that a vehicle emits. Assigned by the US EPA or another pollution monitoring agency.


The angle at which the car's tires contact the road. Alignment is very important for safety. A car that is out of alignment will wander the roadway, be difficult to steer under varying load and road surface conditions and will suffer from increased tire wear. Alignment should be checked every time tires are changed.



The distribution of rotating mass around the axle. Balance is adjusted by adding weights to the wheel so that the weight of the tire and wheel assembly is evenly distributed around the axle. A bouncing sensation while driving may be a tire out of balance. Uneven tire wear results from an out of balance condition.


Friction devices used to slow wheel rotation and thus reduce vehicle speed. May be disc or drum type. Disc brakes apply friction to a rotating disc and are common on front wheels. Drum brakes are still found on older vehicle rear wheels. Drum brakes apply pressure outward to the interior surface of a rotating cylinder.


Catalytic converter

An emission control device installed in the exhaust stream of a vehicle to reduce NOx emissions. Exhaust gasses pass through a catalyst screen that chemically changes smog producing compounds into inert by-products.

Climate control

Describes the control systems that regulate heating and air conditioning in the cabin. Climate control can include automatic temperature controls, surface heating, and air distribution. Differs from the air-conditioning system which is the system to mechanically cool cabin air.

Coolant (antifreeze)

The chemical, mixed with water, that circulates in the interior of the engine to carry heat away from the cylinders and engine block. The coolant is circulated by the water pump and is cooled in the radiator where engine heat is transferred to the outside air.

Curb weight

The weight of the vehicle as it sits, ready to drive. Generally includes full fluids but does not include passengers or baggage.


The space inside the engine that contains the piston. Combustion takes place in the cylinder. The valves and spark plugs protrude into the cylinder.



The computer generated and monitored data that is used by mechanics to determine operating condition of the vehicle. Diagnostic computers monitor the ignition, timing, emissions, transmission and other operating parameters and generate "check-engine" lights and other warnings. Mechanics interface with the car's diagnostic systems through the Onboard Diagnostic (OBD) port.


The structures of the vehicle that transfer power from the engine to the wheels. Includes transmission, drive shaft, differential, and axle.



The general term for the gasses that are released as a by-product of internal combustion. Include water vapor, Carbon Dioxide, Nitrogen compounds, Sulfur compounds and Hydrocarbons. Emissions are the compounds related to smog and health or environmental concerns.

Engine displacement

A measure of the volume of space available in the cylinders for combustion. A larger volume, higher displacement engine will have more space for combustion and will produce more power and use more gas. Usually given in terms of cubic inches or cubic centimeters.



The general term for the fluid substances required to keep a vehicle running. Includes engine oil, power steering fluid, brake fluid, and coolant. These fluids must be checked and replaced at the recommended interval in order to maintain vehicle safety and reduce wear.

Fuel economy

A measure of the distance a car will travel using a given amount of fuel. An indirect measure of a car's efficiency. Typically stated as Miles Per Gallon (MPG) to indicate the number of miles the car will travel for each gallon of fuel purchased. This figure is variable depending on driving conditions.

Fuel injection

One of the methods by which fuel is introduced into the intake-air stream. In a fuel injection system, a fuel pump sprays fuel through a nozzle into the airflow at the cylinder. This is different from a carburated system wherein low pressure is used to pull fuel into the airstream just outside of the intake manifold.

Fuel system

Includes the fuel tank, filler neck and cap, fuel pump, fuel lines, indicating sender unit and any other parts related to the fuel storage, flow or metering.

Fuel type

There are several kinds of fuel available for automotive use. These include gasoline, diesel, ethanol, E85, and bio-diesel. A vehicle may be compatible with several different types in the same family. For example, a gasoline vehicle may also burn E85. Likewise, diesel and Bio-Diesel may be interchangeable. Engines are designed specifically for the fuel that is called for by the manufacturer and may be damaged by the use of inappropriate fuels. Gasoline and Diesel are both derivatives of crude oil that are separated during fractional distillation. Ethanol can be sourced from petroleum or as a by-product of fermentation of plant material (bioethanol). Fuels labeled as E25, E85, or E100 refer to the percentage of ethanol blended with traditional gasoline.



The gears and gear trains that convert rotating power from the power source to create speed and torque at the wheels. Usage varies and the term may be applied to the transmission as a whole or to the gear assemblies alone.


Global Positioning System, a navigational tool that uses satellite positioning combined with street level databases to locate a vehicle's position and provide directions to the destination



The driving characteristics of a vehicle which include steering feel and responsiveness, cornering and acceleration/deceleration lean, braking effectiveness, traction control, acceleration speed, and maneuverability. Handling is one of the primary ways that car reviews describe a vehicle.


The measure of the output power of an internal combustion engine. May be measured before or after power lost to inefficiencies in the transmission and drive train. Higher horsepower will be a stronger engine that uses more gasoline.


Heating, Ventilation and Air Conditioning.


Jump start

To use another vehicle's battery and electrical system to start a vehicle which has a dead battery. Accomplished using jumper cables to attach the batteries of the two vehicles together.



An anti-theft device that disables the door latches of a vehicle. May be electronically or manually controlled using a fob or a key. Used to secure a vehicle from outside entrance.



The paint, trim-paint, and clear coat used to cover the metal parts of a vehicle's exterior.

Power steering

A steering system that uses hydraulic pressure to boost the steering forces applied to the wheels. Effectively reduces pressure felt by the driver at the steering wheel. System includes a power steering pump, fluid, and mechanical linkages between the steering wheel and the wheels.


All the parts of a vehicle that generate power and deliver it to the road. Includes the power train components. Power train may include the engine, turbochargers, exhaust, transmission, drive shaft, gearbox, differential, final drive, wheels and tires.


Pounds per Square Inch, a measure of pressure. 20 pounds applied to a one square inch area would be described as 20 psi. The same pressure applied over a one-half square inch area would be 40 psi. Can be used to measure fluid pressure.


Seating capacity

The number of seating positions in a vehicle. Often defined by the number of seat belts.

Service book

The manual or set of manuals that define and describe the service required for maintenance and repair of a vehicle. May be included in an owner's manual or may be a comprehensive manual designed for professional use.

Stability control

Stability control is a safety feature that senses inappropriate steering inputs and applies braking correction to individual wheels to prevent oversteer and understeer and the resulting loss of traction.


An air compressor that increases air density in the intake-air stream to increase engine power output. A supercharger is powered by an accessory drive belt or gear from the engine. If the compressor is powered by a turbine in the exhaust stream, it is called a Turbo-supercharger or "Turbocharger".


The shock absorbers, springs, tires, tire air, and linkages that connect a vehicle to the ground and allow for relative motion between the chassis and the wheels. Suspension is designed to cushion the ride of the occupants, to improve handling characteristics and to increase traction.


Tire pressure

The measure of air pressure inside the tire. A commonly overlooked safety item, proper tire inflation is critical to maintaining tire life, correct handling and maintaining traction with the road in variable driving conditions. Tire pressure should be checked and adjusted once a month.

Tire profile

The numbers that represent the size and shape of a tire. For example, a tire sized P225/70R16 is rated for Passenger vehicles, has a width of 225 millimeters, an aspect ratio of 70, is a radial tire, and has a wheel size of 16 inches in diameter. Aspect ratio refers to the tire's height as a percent of its width. Thus, lower aspect ratio tires tend to have improved handling compared to higher aspect ratio tires (race tires are fat compared to street tires).


Force applied to an object (a tire) that causes it to rotate. High power applied at low torque will cause a fast car that does not accelerate quickly. Likewise, high torque will create a quick-accelerating car.

Traction control

The safety features of a vehicle designed to sense changing road conditions and adjust the vehicle to maximize traction. This may include differentially changing power output at the wheels, adjusting brake pressure and perhaps making adjustments to the suspension. Traction control is a sub-component of stability control but does not brake as needed to improve steering control.


A term of varying usage that may include the gears and gear train that converts power from the engine to torque at the wheels. May also include components like the clutch, drive shaft, final drive and differential to describe the system for delivering power to the wheels. Transmissions are typically described as manual or automatic. In a manual transmission, the driver must use the clutch to disengage the drive power before repositioning the drive gear for the optimum gear ratio. In an automatic transmission, the transmission assembly automatically repositions the gears for optimum ratios based on power inputs, speed and selector positioning.


An air compressor that is used to increase air density in the intake-air stream. Similar to a supercharger, a turbocharger is driven by a turbine in the exhaust stream of the engine. The engine must be producing exhaust gasses for the turbocharger to operate. May be controllable thereby allowing the driver to select how much exhaust is driving the turbine and increasing engine power output.


Vehicle type

A classification of vehicles by size, seating capacity, design purpose, styling or some other characteristic. Types may include, sedan, hatchback, economy, convertible, minivan, luxury, hybrid, SUV or pickup. Vehicles may fit in several categories, for example a luxury SUV or a hatchback hybrid.


Vehicle Identification Number, the 17 character number that serves to identify a particular vehicle. The VIN will define where and when the vehicle was built, what type of fuel it uses, serial number and which engine is installed, for example.