SVP Light Vehicle Mechanic key terms

A rigid, adjustable support placed under a raised vehicle's frame or axle to hold it up mechanically. Unlike a hydraulic jack it cannot lose pressure, so it protects you if the jack fails or sinks.

A wedge-shaped block placed against a tyre to stop the vehicle rolling. Chocks are used whenever a vehicle is raised, parked on a slope, or has its parking brake released during service.

A procedure for isolating an energy source, such as a battery or high-voltage system, and fitting a lock and warning tag so the circuit cannot be re-energised while someone is working on it.

A standard document supplied with a chemical that lists its hazards, safe handling and storage rules, first-aid measures, and required protective equipment. Read it before using an unfamiliar product.

A wrench that signals, by click, beep, or display, when a preset tightening force is reached. It lets fasteners be tightened to specification so joints are neither loose nor stretched or stripped.

A precision instrument with a calibrated screw that measures outside dimensions to hundredths of a millimetre. It is used to check shafts, journals, and brake disc thickness against specification.

A set of thin metal blades of known thickness used to measure a small gap, such as valve clearance or spark plug gap, by sliding blades in until one fits snugly.

A check that cranks the engine with ignition disabled and measures peak pressure in each cylinder. Low or uneven readings point to worn rings, leaking valves, or a blown head gasket.

A test that pressurises a cylinder with air at top dead centre and measures how much escapes. Listening at the intake, exhaust, or oil filler identifies where the leak is.

The small gap between the valve stem and the rocker or cam follower when the valve is closed. Too little can hold a valve open; too much causes noise and reduces lift.

A toothed belt that keeps the crankshaft and camshaft rotating in step so valves open at the correct moment. It has a replacement interval and can cause major engine damage if it snaps.

The computer that runs the engine and transmission. It reads sensor inputs, calculates fuel and spark, controls actuators, monitors emissions, and stores fault codes when something is out of range.

A sensor in the intake that measures how much air enters the engine. The computer uses that figure to calculate the right fuel quantity, so a dirty or faulty sensor can cause poor running.

A short- and long-term percentage adjustment the computer applies to injector opening time to keep the air-fuel mixture correct. Positive trim means fuel is being added; negative trim means it is being removed.

An electrically operated valve that sprays a precisely metered amount of fuel into the intake port or directly into the cylinder, opened by a pulse from the engine computer.

A sensor in the exhaust that produces a signal reflecting how much oxygen remains in the exhaust gas. The computer uses it to fine-tune fuel delivery and to judge catalyst efficiency.

A sealed network of hoses, a charcoal canister, and a purge valve that captures fuel vapour from the tank and burns it in the engine instead of releasing it to the atmosphere.

A device in the exhaust that uses precious metals to convert hydrocarbons, carbon monoxide, and nitrogen oxides into less harmful gases. It works only once hot and can be damaged by misfires or rich mixtures.

A hand-held instrument that measures voltage, resistance, and current. Technicians use it to check battery voltage, trace open circuits, and confirm sensor readings.

A measurement of the voltage lost across a cable, connector, or ground while current flows. A significant drop shows where unwanted resistance is causing slow starting or dim lights.

Current that flows from the battery while the vehicle is switched off and all systems should be asleep. Excessive draw drains the battery overnight and is found by measuring current and pulling fuses.

A two-wire digital network that lets control modules share data quickly with very little wiring. A fault on the bus can disable communication between many systems at once.

A friction assembly that connects and disconnects the engine from a manual gearbox, letting the driver pull away smoothly and change gear while the vehicle is moving.

A joint that lets a driveshaft transmit power through a large angle at constant speed, used at the ends of front-wheel-drive halfshafts. A split boot lets grit in and grease out.

A gear set that splits drive between two wheels while allowing them to turn at different speeds in a corner, and that multiplies torque through its final drive ratio.

Removing air from the hydraulic brake system by opening a bleeder screw and pushing fresh fluid through. Air is compressible and causes a low, spongy pedal.

A system that monitors wheel speed and rapidly releases and reapplies brake pressure to stop a wheel locking, keeping the vehicle steerable during hard braking.

A hygroscopic hydraulic fluid that transmits pedal force to the brakes. It absorbs water over time, which lowers its boiling point, so it must be replaced on schedule.

Adjusting the angles of the wheels relative to the vehicle and the road, mainly toe, camber, and caster, so tyres wear evenly and the vehicle tracks straight.

The tilt of the top of a wheel inward or outward from vertical when viewed from the front. Excessive camber causes uneven tyre wear and affects cornering grip.

A pivoting joint made of a stud in a socket that connects the control arm to the steering knuckle, allowing suspension movement and steering to happen together.

The fluid in an air-conditioning system that absorbs heat when it evaporates in the cabin evaporator and releases it at the condenser. It is handled in a closed, recovered loop.

The service procedure that removes refrigerant from a system, weighs it, pulls a vacuum to remove moisture and check for leaks, then refills the exact specified charge.

A pleated filter that removes dust and pollen from air entering the passenger compartment. A clogged one reduces airflow and can cause misting and odours.

An alphanumeric code stored by a control module when a monitored circuit or system falls outside its expected range. It names the fault area but not necessarily the failed part.

A device that connects to the vehicle's diagnostic socket to read fault codes and live sensor data, and to command tests on control modules.

A snapshot of sensor readings and operating conditions captured at the moment a fault code was set, which helps recreate the fault when it does not occur in the workshop.

A standardised on-board diagnostic standard that defines the 16-pin test connector, fault code structure, and emissions monitors required on light vehicles.

The distance or time set by the manufacturer at which specified maintenance, such as oil and filter changes, is due. Intervals vary with operating conditions and duty cycles.

A structured checklist used during a service to examine tyres, brakes, fluids, belts, lights, and suspension so developing faults are found before they become failures or safety risks.