Car glossary

Brakes and safety

ABS

Anti-lock braking system

Modulates braking pressure to limit wheel lock. It helps retain steering control within available grip.

Hybrids and electric vehicles

AC / DC / OBC

Charging and on-board charger

During AC charging, the on-board charger converts current for the battery. DC charging supplies direct current to the battery system.

Suspension and steering

Adaptive damping

Changes damper characteristics according to control inputs and conditions. It does not necessarily imply air suspension.

Brakes and safety

ADAS / AEB / ACC

Advanced driver assistance systems

ADAS includes functions such as automatic emergency braking (AEB) and adaptive cruise control (ACC). It does not mean autonomous driving.

Emissions and exhaust

AdBlue

Fluid for the SCR system

A urea-based fluid dosed into the exhaust to reduce NOx in the SCR system. It goes into its dedicated tank, not the diesel fuel.

A warning can concern fluid level or a system fault. Topping up does not automatically fix sensor or dosing problems.

Electrics and ignition

AGM / EFB

Lead-acid battery technologies

Battery technologies often used with start-stop. Replacement must meet vehicle requirements, including registration or adaptation when specified.

Suspension and steering

Air suspension

Uses air springs with an air supply and control system. Some systems automatically adjust ride height.

Cooling and air conditioning

Air-conditioning compressor

Compresses and circulates refrigerant. It may be engine-driven or electrically powered.

Cooling and air conditioning

Air-conditioning condenser

Releases refrigerant heat to the surroundings, helping it change from gas to liquid.

Cooling and air conditioning

Air-conditioning evaporator

Absorbs heat from air entering the cabin. Its cold surface can condense moisture from the air.

Electrics and ignition

Alternator

Converts mechanical energy into electrical energy for vehicle loads and battery charging where fitted.

Suspension and steering

Anti-roll bar

Couples suspension movement across an axle to limit body roll in corners. Drop links transfer forces to the suspension.

Tyres and wheels

Aquaplaning / hydroplaning

Occurs when a water layer separates the tyre from the road, reducing control. Speed, water, tread and pressure affect risk.

Transmission and drivetrain

AWD / 4WD / 4x4

All-wheel / four-wheel drive

Names for systems capable of driving both axles. Continuous or selectable operation and limitations vary by model.

Hybrids and electric vehicles

BEV

Battery electric vehicle

Uses one or more electric motors powered by a battery. Energy is replenished by charging and can be recovered during deceleration.

Hybrids and electric vehicles

BMS

Battery management system

Monitors and manages the battery, including operating limits and, depending on the system, cell balancing. High-voltage work requires qualified personnel.

Brakes and safety

Brake caliper

Applies brake pads to the disc using pistons and its mechanism. Sticking can cause abnormal wear and heating.

Brakes and safety

Brake fluid

Transmits pressure through the hydraulic circuit. Use the required specification; DOT classes do not imply universal compatibility.

Brakes and safety

Brake pads and discs

Convert motion into heat through friction. Wear is assessed by inspection and measurement, not mileage alone.

Engine and timing

Camshaft

Controls valve opening through cam profiles. The timing drive synchronizes it with the crankshaft.

Diagnostics and identification

CAN bus

Controller Area Network

A network used by vehicle modules to exchange messages. Communication faults can involve power supply, wiring or modules.

Intake, fuel and sensors

Charge-air cooler

Cools compressed air before it enters the engine. Heat may be transferred to outside air or a liquid circuit.

Transmission and drivetrain

Clutch

Engages and disengages torque transfer between engine and transmission. Type and actuation vary with the transmission.

Engine and timing

Combustion misfire

Missing or inadequate combustion in a cylinder. Causes can involve ignition, fueling or compression, not just a spark plug.

Intake, fuel and sensors

Common-rail injection

A system with a high-pressure fuel rail supplying the injectors. Never loosen pressurized fuel lines.

Engine and timing

Compression pressure

Cylinder pressure measured using a defined test. Results depend on the procedure and must be compared with engine specifications.

Cooling and air conditioning

Coolant expansion tank

Accommodates coolant volume changes. Opening a pressurized system when hot can cause burns.

Cooling and air conditioning

Coolant pump

Circulates coolant. It may be mechanically or electrically driven depending on the vehicle and circuit.

Cooling and air conditioning

Coolant thermostat

Regulates coolant flow through the radiator to control engine temperature. Some versions have electronically assisted control.

Engine and timing

Crankshaft

Converts piston motion through connecting rods into rotation. Its position is also used by engine management.

Transmission and drivetrain

CVT

Continuously variable transmission

Varies the transmission ratio without conventional fixed gear steps. Design and fluid requirements depend on the model.

Engine and timing

Cylinder-head gasket

Seals the block-to-head joint, separating combustion chambers and oil and coolant passages.

Transmission and drivetrain

DCT / DSG

Dual-clutch transmission

Uses two clutches for separate gear groups. DSG is a trade name; versions may use dry or wet clutches.

Transmission and drivetrain

Differential

Allows speed differences between connected wheels or shafts while transmitting torque.

Emissions and exhaust

DPF

Diesel particulate filter

Traps particles from a diesel engine’s exhaust. Regeneration burns soot under manufacturer-defined conditions.

A warning does not automatically justify forced regeneration. Check loading, sensors and the cause; burning soot does not remove ash.

Emissions and exhaust

DPF soot regeneration

A process oxidizing accumulated soot. It does not remove ash or automatically fix sensors or the cause of excessive loading.

Transmission and drivetrain

Drive shaft / CV axle

Transfers torque to a wheel while accommodating suspension and, where applicable, steering movement. Boots protect the joints.

Diagnostics and identification

DTC

Diagnostic trouble code

A code saved by a vehicle controller when it detects an abnormal monitored condition.

It describes what the system detected, not proof of the part that must be replaced.

Transmission and drivetrain

Dual-mass flywheel

Uses two masses and spring elements to reduce torsional vibrations transmitted to the gearbox.

Transmission and drivetrain

e-CVT

Hybrid continuously variable transmission

A name used for some hybrid transmissions coordinating the engine and electric machines. It does not automatically imply a CVT belt.

Brakes and safety

EBD

Electronic brakeforce distribution

Adjusts brakeforce distribution according to detected conditions, typically using ABS components.

Diagnostics and identification

ECU / ECM / PCM

Electronic control unit

A controller that processes signals and commands vehicle functions. ECM controls the engine; PCM may also manage the transmission.

Emissions and exhaust

EGR

Exhaust gas recirculation

Returns a controlled portion of exhaust gas to the intake to reduce nitrogen oxide (NOx) emissions.

P0401 alone does not prove a faulty valve: deposits, restricted passages, control or measurement faults are possible.

Cooling and air conditioning

Engine coolant / antifreeze

Fluid formulated for heat transfer and freeze and corrosion protection. Check compatibility by specification, not colour alone.

Engine and timing

Engine power

Expresses the rate at which an engine can perform mechanical work. kW and horsepower measure power, not torque.

Cooling and air conditioning

Engine radiator

Transfers heat from coolant to the air. It is different from the air-conditioning condenser.

Engine and timing

Engine torque

Measures the engine's turning effect, commonly in newton-metres. Interpret it alongside engine speed and gearing.

Brakes and safety

EPB

Electric parking brake

Electrically operates the parking brake. Component replacement may require service mode and the vehicle-specific procedure.

Suspension and steering

EPS

Electric power steering

Assists steering effort using an electric motor. Do not confuse it with ESP, which manages vehicle stability.

Brakes and safety

ESP / ESC / DSC

Electronic stability control

Compares vehicle motion with the intended direction and can brake individual wheels or reduce torque to limit skidding.

Emissions and exhaust

EVAP

Evaporative emissions control

Captures and manages fuel vapour using components such as an activated-carbon canister and purge valve.

Emissions and exhaust

Exhaust catalyst

Promotes chemical reactions reducing certain exhaust pollutants. Its exact function depends on catalyst type and engine.

Emissions and exhaust

Exhaust oxygen sensor

Measures residual exhaust oxygen for mixture control or exhaust-treatment monitoring, depending on position and system.

Emissions and exhaust

FAP

Filtre à particules

The French term for a particulate filter, commonly used for the same filtering function as DPF.

Some systems use a separate regeneration additive. This is not AdBlue; the specification and procedure depend on the vehicle.

Diagnostics and identification

Freeze-frame

Fault snapshot

A set of parameters saved by the ECU for a diagnostic event; availability varies.

Save it before clearing and check the associated DTC. It is different from live data.

Intake, fuel and sensors

Fuel injector

Meters and atomizes fuel. Location, pressure and control differ between port injection, direct injection and diesel systems.

Electrics and ignition

Fuse / relay

A fuse protects against overcurrent; a relay switches a circuit through a control input. Never substitute an oversized fuse.

Transmission and drivetrain

FWD / RWD

Front-wheel / rear-wheel drive

FWD drives the front wheels, while RWD drives the rear wheels. These terms do not always describe engine position.

Intake, fuel and sensors

GDI / direct injection

Gasoline direct injection

Injects gasoline directly into the combustion chamber using high-pressure fuel supply and injectors.

Electrics and ignition

Glow plug

Provides local heating to support diesel starting and operation, depending on control strategy. It does not produce a gasoline spark plug's spark.

Emissions and exhaust

GPF / OPF

Gasoline particulate filter

Traps particles in the exhaust of certain gasoline engines. Not every gasoline engine has this filter.

Hybrids and electric vehicles

HEV

Non-plug-in hybrid

Combines combustion and electric propulsion. The battery charges through recovery and engine energy without external plug-in charging.

Intake, fuel and sensors

HPFP

High-pressure fuel pump

Raises fuel pressure for direct injection. It is separate from the tank supply pump where one is fitted.

Electrics and ignition

Ignition coil

Transforms electrical energy into high-voltage pulses for spark plugs. A misfire alone does not prove a faulty coil.

Hybrids and electric vehicles

kW / kWh

Power versus energy

kW measures power; kWh measures energy. Battery capacity in kWh is not the same quantity as charging power in kW.

Diagnostics and identification

Live diagnostic data

Values read by a scan tool during operation. Interpretation requires units, test conditions and appropriate reference values.

Tyres and wheels

Load and speed ratings

Markings indicating load and speed capability under defined operating conditions. Check them against vehicle requirements.

Electrics and ignition

Low-voltage battery

Powers accessories, control systems and, depending on design, starting. It may also be required in electric vehicles.

Diagnostics and identification

LTFT

Long-term fuel trim

A learned fuel-delivery adjustment. Assess it alongside STFT; a single value does not establish the cause of a fault.

Intake, fuel and sensors

MAF

Mass airflow sensor

Measures intake air mass for fueling calculations and other engine-control strategies.

Intake, fuel and sensors

MAP

Manifold absolute pressure sensor

Measures absolute intake-manifold pressure. Absolute pressure includes atmospheric pressure, unlike gauge boost pressure.

Hybrids and electric vehicles

MHEV

Mild hybrid

An electrical system assists the engine and can recover energy. Electric-only driving capability depends on the architecture and may be absent.

Diagnostics and identification

MIL / Check engine

Malfunction indicator lamp

A lamp indicating a fault monitored by the engine/emissions system. It does not identify the failed component by itself.

Diagnostics and identification

OBD / OBD-II

On-board diagnostics

A system that monitors and reports faults. OBD-II standardizes access to some emissions-related data and trouble codes.

Maintenance and parts

OE / OEM

Original equipment / equipment manufacturer

Terms relating to original equipment and its manufacturer. An OEM label in an advert does not alone prove part identity or compatibility.

Maintenance and parts

Oil performance specifications

Classifications and approvals describe requirements beyond viscosity. Choose a product meeting the engine's exact requirements, not merely a familiar brand.

Maintenance and parts

Oil, air, fuel and cabin filters

Trap contaminants in different circuits. The cabin filter cleans passenger air; it is not the engine air filter.

Maintenance and parts

Part number

Identifies a part or catalogue version. Fitment may require VIN, engine code, equipment and checking superseded references.

Emissions and exhaust

PCV

Positive crankcase ventilation

Manages gases entering the crankcase and routes them to the intake, with oil separation depending on the design.

Diagnostics and identification

Pending trouble code

Indicates a detected abnormality that has not yet met all confirmation criteria. Confirmation conditions depend on the monitor.

Diagnostics and identification

Permanent emissions trouble code

On supporting systems, this code cannot simply be cleared by a scan tool; the controller must verify repair through its monitor.

Hybrids and electric vehicles

PHEV

Plug-in hybrid

Combines combustion and electric propulsion with a battery that can also charge from an external supply.

Diagnostics and identification

PID

Parameter identifier

Identifies diagnostic information such as engine speed or temperature. Available parameters vary between vehicles and scan tools.

Engine and timing

Piston

A moving cylinder component receiving gas pressure and transferring force to the connecting rod. Rings help seal combustion and control oil.

Diagnostics and identification

Readiness

Emissions self-test status

Shows whether supported emissions monitors have run their required checks.

Incomplete does not automatically mean a fault or deception; it may follow a reset or unmet test conditions.

Maintenance and parts

Reconditioned / remanufactured part

A reused part following work and checks. Process scope varies; request work details, test results, warranty and return terms.

Diagnostics and identification

Reduced-performance mode

A strategy limiting power or certain functions after a fault is detected. It does not guarantee that continued driving is safe.

Hybrids and electric vehicles

Regenerative braking

Uses the electric motor as a generator to recover some energy. Effectiveness and strength also depend on battery conditions.

Maintenance and parts

Replacement-market parts

Parts sold for replacement by various manufacturers. Assess quality and compatibility for the exact product, not just its category.

Maintenance and parts

SAE / viscosity

Oil viscosity grade

A marking such as 5W-30 describes cold and hot viscosity behaviour. It does not alone confirm engine approval.

Maintenance and parts

Scheduled servicing

Operations scheduled by time, mileage and use conditions. An oil change does not automatically cover all work due.

Emissions and exhaust

SCR

Selective catalytic reduction

An exhaust-treatment system reducing nitrogen oxides using a catalyst and, commonly in cars, AdBlue.

Suspension and steering

Shock absorber / damper

Damps suspension oscillations. In conventional suspension, the spring supports the load and the damper controls movement.

Hybrids and electric vehicles

SOC

State of charge

An estimate of available energy or charge relative to a reference capacity. The displayed percentage is not battery health.

Hybrids and electric vehicles

SOH

State of health

An estimate of degradation against a reference. Methods may use capacity, resistance or other indicators and vary between systems.

Electrics and ignition

Spark plug

Produces the spark igniting the mixture in spark-ignition engines. Type and electrode gap must suit the engine.

Brakes and safety

SRS / Airbag

Supplemental restraint system

Includes airbags and, depending on the vehicle, pretensioners and sensors. It supplements seat belts rather than replacing them.

Electrics and ignition

Starter motor

Cranks the combustion engine for starting. Some hybrid systems use another electric machine for this function.

Diagnostics and identification

STFT

Short-term fuel trim

A rapid fuel-delivery adjustment during mixture control. Direction and magnitude must be interpreted for the engine and operating conditions.

Suspension and steering

Suspension control arm

Guides wheel movement and carries forces through joints and bushings. Play can affect alignment and handling.

Suspension and steering

Suspension spring

An elastic element supporting the vehicle and allowing wheel movement relative to the body. Several designs exist.

Brakes and safety

TCS / ASR

Traction control

Limits driven-wheel spin through torque and/or brake intervention. It cannot create grip where none is available.

Intake, fuel and sensors

Throttle valve

Regulates airflow through the intake. Its precise role differs between gasoline and diesel engines.

Engine and timing

Timing belt

A toothed belt synchronizing the timing system. Replacement intervals and required parts depend on the engine and manufacturer schedule.

Engine and timing

Timing chain

A chain driving the timing system with guides and tensioners. It is not automatically immune to wear or maintenance needs.

Transmission and drivetrain

Torque converter

Transfers torque through fluid in certain automatic transmissions. A lock-up clutch can reduce slip under suitable conditions.

Tyres and wheels

TPMS

Tyre pressure monitoring system

May measure pressure with sensors or infer losses from wheel speeds. Reset procedures depend on the system.

Transmission and drivetrain

Transfer case

Distributes torque between axles in certain all-wheel-drive systems. Not every AWD architecture uses one.

Transmission and drivetrain

Transmission mechatronics

An assembly combining electronic control and transmission actuators. Configuration and repair options depend on the transmission.

Intake, fuel and sensors

Turbocharger

Uses exhaust-gas energy to drive a compressor that supplies pressurized air to the engine.

Intake, fuel and sensors

Turbocharger bypass valve

Diverts some exhaust gas around the turbine to control boost. It is different from a variable-geometry mechanism.

Tyres and wheels

TWI

Tread wear indicator

A small raised bar in tyre grooves helping assess wear. Also check cuts, bulges and uneven wear.

Tyres and wheels

Tyre manufacturing date

The four-digit date code indicates manufacturing week and year. The date alone does not describe the tyre's physical condition.

Tyres and wheels

Tyre size marking

In 205/55 R16, 205 is nominal width in mm, 55 the aspect ratio percentage, R radial construction and 16 rim diameter in inches.

Intake, fuel and sensors

Variable-geometry turbocharger

Adjusts exhaust flow into the turbine using movable elements to suit engine operating conditions.

Diagnostics and identification

VIN

Vehicle identification number

A vehicle identifier, usually 17 characters on modern cars. Decoding does not provide an accident or mileage history.

Engine and timing

VVT

Variable valve timing

Changes valve opening and closing timing according to operating conditions. Mechanism and control vary by engine.

Engine and timing

Wet timing belt

A timing belt designed to run in engine oil. Correct oil specification and engine-specific service procedures are essential.

Suspension and steering

Wheel alignment

Checks and adjusts angles such as toe, camber and caster where adjustable. It is different from wheel balancing.

Tyres and wheels

Wheel balancing

Compensates for uneven mass distribution in the wheel-and-tyre assembly. It may reduce vibration but does not replace alignment or wear checks.