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Displaying 101 - 150 of 502 glossary terms Use the search function to find terms.
Counter Shaft

Counter Shaft in the manual gearbox is the shaft that carries the power of the clutch shaft to the driveshaft. It is turning opposite to the gears.

Counter Weight

Counterweight refers to a weight added to rotating shafts or wheels to balance and neutralize vibration. These are on the crankshaft, wheels, flywheel, and driveshaft.


Cowl refers to a portion between the car body and the engine compartment. Usually, this is the cover that sits under the windshield wipers.


CPO means Certified Pre-Owned vehicles which are closely inspected and have to meet standards to qualify as certified pre-owned vs. a used car. A CPO vehicle often comes with vehicle warranties.… Read more

Crank Case

A Crank Case is the lower part of the engine block that encases the crankshaft and its bearings.

Crank Shaft

Crank Shaft is essentially the backbone of the internal combustion engine. The Crank Shaft is responsible for the engine's proper operation, and it converts a linear motion to a rotational… Read more

Crankcase Breather

Crankcase Breather is a valve that releases excessive crankcase pressure.


Crankshafts are rotating shafts that are used to convert the reciprocating motion of pistons into rotational motion. Crankshafts are used in internal combustion engines and consist of a series of… Read more

Cruise Control

A Cruise Control system automatically controls a vehicle's speed. This mechanical servo system takes over the throttle to maintain the speed set by the driver.

Crumple Zone

Crumple Zone is the area that collapses during an impact to reduce energy from the collision and avoid bodily injury.

Curb Weight

The Curb Weight is its empty weight without passengers or cargo, resting on a flat surface.

Curtain Airbags

Curtain Airbags are installed on the side of the vehicle. During an impact, it will unfold and protect the occupant's head and upper body.

Cuts Out

Cut Out is a loss of power of the engine. The engine could misfire, and it feels like an engine shut off.

CV Joint

Constant Velocity Joint or CV allows a driveshaft to transmit power through an irregular angle during rotational speed without increased friction or play.

CV Joint Boot

CV Joint Boots prevent water and debris from entering the joint and contaminating it.


CVT Transmissions have endless gear ratios. The engine runs at a constant speed without having to change gears. The goal is to maximize engine efficiency. A CVT transmission has a longer… Read more


Cylinder refers to the cylindrical shape inside the engine block. It is the surface on which the piston moves and compresses the air-fuel mixture, measured in cm or inches. It is typically cast… Read more

Cylinder Head

Cylinder Head is an aluminum or iron-casted device which holds the intake manifold, the exhaust manifold, and houses on the valvetrain. Depending on the configuration, it may also house the… Read more


D-Pillar is the rearmost roof that supports the structure on an SUV, minivan, or wagon.


Damping is used in vehicles to absorb motions on rough surfaces and is usually done on shock absorbers. It also controls oscillations. Heavy-duty trucks and some high-end cars use air suspensions… Read more


Dashboard refers to the panel right under the windshield. It holds gauges and switches and houses the glove box.


decibels A (dBA) is a measurement unit for sound. It measures the sound's volume or the signal's strength, computed as the signal-to-noise ratio.

DC Current

Direct Current (DC) electricity uses electrons that move in only one direction. Cars operate on 12 volt DC. In contrast to AC's wave motion, this current moves linearly.

Dead Axle

Dead Axle is a non-driven axle that is often on the rear of an FWD vehicle.


Deceleration refers to the changing velocity of the car during a break.

DEF Fluid

Diesel Exhaust Fluid (DEF), also called "Aqueous Urea Solution" and in others "AdBlue," is a transparent, colorless, non-toxic, and virtually odorless liquid that is injected… Read more


Depreciation is the loss in value that a vehicle incurs when it is purchased and used.


Detonation is an explosion of the unburned fuel-air mixture in the combustion chamber that burns from the heat created from the ignited spark. It creates an engine knock which is very stressful… Read more

Diesel Particulate Filter

Diesel Particular Filter filters particles from the burned exhaust gases. Those filters need maintenance.


Differential delivers driving force to the wheels while the wheels spin at different speeds due to road conditions. It makes the wheels attached to the suspension act independently.

Digital Multimeter

Digital Multimeter is a necessary tool for testing, diagnosing, and troubleshooting electrical circuits, components, and devices.


Dipstick refers to a rod the measures the oil level in vehicles. Those are calibrated specifically to the vehicle and can't be interchanged with other models. In some cases, dipsticks are… Read more

Direct Injection System

Direct Injection is injected directly into the combustion chamber using a fuel injector. A high-temperature injection nozzle is placed for each cylinder.


Direct Shift Gearbox, also called Dual-Clutch Gearbox, is an alternative to automatic transmissions.


Displacement is the volume measurement of the combined cylinders. It is measured when the cylinders are in the downward position.


Distributor refers to a device that distributes the ignition to each cylinder. Inside the distributor cap is a shaft installed driven by a gear connected to the cam to pass the high voltage… Read more

Distributor cap

Distributor Cab is over the distributor and its rotor. It has a connector for sparkplug wires. The rotor moves inside the cap and distributes voltage to each cylinder.


Department of Motor Vehicles, or DMV, is a state-level agency responsible for vehicle registration and licensing.


Dual Overhead Camshafts is an engine with two camshafts that are usually located in the cylinder head.

Door Ajar

Door Ajar Warning Light indicates a door is open. This warning light will come on in red if a door is not securely closed. It will turn off when the door is securely closed.

Drag Coefficient

Drag Coefficient (commonly abbreviated as cd, cx, or cw) refers to measuring an object's resistance or drag in a fluid environment, such as water or air. Any verticle surface adds to the… Read more

Drive Axle Boots

Drive Axle Boots are made of rubber which holds a grease filling that lubricates the flexible bearings and joints inside the boots.

Drive Belt

Drive Belts transfer the rotation of the crankshaft to other devices such as the alternator, air conditioning compressor, and mechanical driver water pumps. A flexible is used for this application… Read more

Drive Belt Tensioner

Drive Belt Tensioner refers to a self-adjusting device that keeps the drive belt properly under tension and reduces maintenance costs.

Drive Shaft

Drive Shaft is a hollow tube to deliver power and torque to the drive axle or differential. In a vehicle, the drive shaft, also known as the propeller shaft, is used to transfer torque from the… Read more


Driveline refers to the drivetrain minus the transmission, meaning it includes only the driveline components. A vehicle's driveline is the means by which power is transferred from the engine… Read more


Drive Shaft is a hollow tube to deliver power and torque to the drive axle or differential. In a vehicle, the drive shaft, also known as the propeller shaft, is used to transfer torque from the… Read more


Drivetrain refers to everything from engine output to the wheels meaning the following components: Clutch, gearbox or automatic transmission, universal driveshaft joints, differentials. All the… Read more

Driving Lights

Driving Lights are the low beam auxiliary lights that are used in normal traffic.

Drum Brake

Drum Brakes are vehicle brakes in which the brake shoes press against the inside drum of the wheel. Drum brake systems consist of hydraulic wheel cylinders, brake shoes, and a brake drum. When the… Read more