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Displaying 301 - 350 of 502 glossary terms Use the search function to find terms.
Multileaf Spring

Multileaf Spring is a leaf spring with several leaves bundled together by steel bands.

Multilink Suspension

Multi-link Suspension refers to a suspension design used in independent suspensions, consisting of one or more longitudinal arms and three or more lateral arms. The front suspension consists of… Read more

Natural Gas Engine

Natural Gas Engine is internal combustion that burns natural gas. Most vehicles upgrades to this option for better fuel economy.

Navigation System

Navigation System guides you to a requested location using satellites to help the driver.


National Highway Traffic Safety Administration (NHTSA, pronounced "NITZ-ah") is an agency of the Department of Transportation within the U.S. federal government. The organization's… Read more


Nightvision is an exterior camera that uses infrared technology to provide added visibility when driving in the dark.


A set of transitional and initially voluntary "national low emission vehicle" (NLEV) standards was used starting in 1999 for northeastern states and 2001 in the rest of the country until… Read more


The newton-meter (also newton meter; symbol N⋅m or N m) is a unit of torque (also called moment) in the SI system. The newton-meter is equal to the torque generated by a force of one newton… Read more


Nitrous oxide refers to a fairly inert oxide of nitrogen that has many uses as an oxidizer for rockets and car engines.


O-Ring is used in groves to provide sealing. It is a ring form made of rubber.


The OBD-II standard is a type of diagnostic connector, pinout the electrical signaling protocols available and the messaging format. On-board diagnostic is an automotive term referring to a… Read more


Octane is the number that indicates the anti-knock quality of the gasoline.


Odometer refers to the instrument located in the dashboard to measure the speed driven.


OEM stands for Original Equipment Manufacturing. Usually refers to components used to build the vehicle at the factory and available for service replacement through franchised dealers.


Over-Head valve (OHV) is positioned directly above the piston in a valve-in-head engine.

Oil Filter

Oil Filters work by filtering dirt and debris from engine oil as it is being lubricated.

Oil Level Low

Oil Level Low indicates that there might be somewhere an oil loss. Regularly check the oil level.

Oil Light

Oil Light indicates a low oil level. After starting the engine, it should turn off right after, and if the oil level is low, the light will turn on. Turn the engine off asap to avoid damage. Check… Read more

Oil Pan

Oil Pan refers to the lowest part of the engine block. It is attached to the engine block and can be detached from the engine block. It serves as a reservoir for engine oil.

Oil Pressure Warning

Oil Pressure Warning means that your engine has excessive or low oil pressure. The problem can be caused by a blocked filter, a blocked oil gallery, or the wrong grade of oil. Low oil pressure… Read more

Oil Pump

Oil Pump is an engine-driven pump installed inside the oil pan to pump oil to the moving engine parts.

One-touch Windows

One-touch Window switches are configured to raise or lower the window glass with one touch.


Overdrive refers to the highest gear in the transmission. It allows the engine to operate at a lower RPM for a given road speed. It will enable the vehicle to achieve better fuel efficiency and… Read more

Overhead Cam

Overhead Camera is a camshaft installed above the cylinder head instead of inside of the engine block.

Overhead Valve

Overhead Valves are in which the valves are installed directly over the pistons.

Overpressure Safety Switch

Pressure Relief Valve (PRV) refers to a type of safety valve that controls or limits the pressure in a system; otherwise, it could build up. A switch will be an example on a turbocharged engine… Read more


Oversteer refers to when a car turns more than the steering direction of the driver.

Oxygen Sensor

Oxygen Sensor, also called the O2 sensor is an input sensor that reports to the ECU. It gives feedback and the air-fuel mixture burned by the engine. Usually, the exhaust system has two sensors.… Read more

Parking Assist

Parking Assist refers to an automated parking aid that helps the driver park very well using guidance system technology.

Parking Brake

Parking Brakes, also known as emergency brakes (e-brakes), are mechanisms that keep a vehicle in place.

Parking Lights

Parking Lights are used once the light switch moves to the first stage. In modern cars, this is also referred to as daylight running light. It increases the visibility of the vehicle.

Parking Sensors

Parking Sensors are installed in the rear and front bumpers to measure the distance to nearby cars or objects while parking in a spot. The driver gets warned by a sound or light.

Particulate Filter

Diesel Particulate Filter (DPF) catches and stores exhaust soot (some refer to them as soot traps) to decrease emissions from diesel cars. Due to their limited capacity, this trapped soot needs to… Read more


Payload Capacity refers to how much weight a vehicle can carry inside its cabin or truck bed. Anything you put inside your vehicle, whether the cargo or passengers, counts towards the vehicle… Read more


Positive Crankcase Ventilation (PCV) system removes harmful gases from the engine’s crankcase and burns those gases in the cylinders. Positive crankcase ventilation devices allow the venting of… Read more

Penetrating Oil

Penetrating Oil, known as penetrating fluid, is a very low-viscosity oil that can free rusted mechanical parts to remove them.


Petroleum is a naturally occurring, yellowish-black liquid that forms underneath the Earth's surface. A complex mixture of hydrocarbons and small amounts of other elements occurring in nature… Read more


Pillars refer to the vertical or near-vertical pillars supporting the windshield or the car's greenhouse, referred to as the A, B, C, or (in larger cars) D-pillars, from front to rear.

Pilot Bearing

Pilot Bearings are located between the engine and clutch and allow the transmission shaft to rotate at a different speed than the crankshaft. By the main bearings, the shaft is suspended and… Read more


Piston refers to a component of reciprocating engines, reciprocating pumps, gas compressors, and pneumatic cylinders, among other similar mechanisms. It is the moving component that contains a… Read more

Plenum Chamber

Plenum Chamber is a portion of the intake manifold system on an engine that delivers air. The chamber is in between the throttle body and the runners of an intake manifold.


Pound-Feet are the units of measurement for torque. Force is produced when a one-pound force is applied to the end of a one-foot-long lever.

Power Loss

Power Loss is referred to the engine's runs and reduced speed while the throttle is held constantly.

Power Steering

Power Steering is a system that uses hydraulic fluid or electrical assistance to reduce the driver's efforts in using the steering wheel at lower speeds. Once the speed increase, the Power… Read more

Power Steering Fluid

Power Steering Fluid is often called ATF 9 automatic transmission fluid, and its color is red.


Powertrain refers to engine, transmission, driveshaft, differential, and axles to deliver power to the wheels.


Pounds per Square Inch (PSI) refers to a standard measurement of pressure.


Pulley refers to a rotating driven device that holds the drive belt.

Purge Valve

Purge Valves are part of the vehicle's Evaporative Emission Control (EVAP) system. The system stops fuel vapors in the fuel tank from escaping into the atmosphere. The EVAP system holds fuel… Read more


Pushrod refers to a metal rod to operate valves in a cylinder head in which the camshaft is attached in the engine block.