Cert III Automotive Mechanic key terms

A procedure for shutting off and physically locking an energy source, such as battery power or compressed air, and attaching a warning tag so nobody can restart the equipment while work is in progress.

Items worn by a technician to reduce injury risk, including safety glasses, gloves, hearing protection, steel-capped boots and respirators, selected according to the hazards of the task.

A standard document supplied with a hazardous chemical that lists its hazards, safe handling, first-aid measures, spill response and disposal requirements, used to plan safe workshop practice.

Sorting workshop waste into separate streams such as used oil, coolant, solvents, batteries and metal scrap so each can be recycled or disposed of through approved channels.

A wrench that measures and limits the twisting force applied to a fastener, used where a manufacturer specifies a torque setting to prevent under-tightening or thread and component damage.

A fastener designed to be tightened past its elastic limit using a specified torque plus angle, giving consistent clamping force; it must be replaced rather than reused after loosening.

A precision measuring instrument with a calibrated screw that measures outside dimensions such as shaft or journal diameter to hundredths of a millimetre or thousandths of an inch.

A measuring tool with sliding jaws and a graduated scale used to read outside, inside and depth dimensions, commonly applied to brake disc thickness and component clearances.

A set of thin metal blades of known thickness used to measure small gaps, such as valve clearance, spark plug gap or ring end gap.

The operating sequence of a petrol or diesel engine in which each cylinder completes intake, compression, power and exhaust strokes, with the crankshaft turning twice per full cycle.

A diagnostic check that measures peak cylinder pressure with a gauge while the engine is cranked, helping identify worn rings, leaking valves or a failed head gasket.

A test that supplies compressed air to a cylinder at top dead centre and measures the percentage lost, with escaping air located at the intake, exhaust, dipstick tube or radiator to pinpoint the fault.

The specified gap between the valve stem and its rocker or cam follower, needed so valves close fully when the engine is hot and measured with a feeler gauge during service.

A sealing component clamped between the cylinder head and engine block that contains combustion pressure and separates coolant and oil passages from each other and from the cylinders.

Uneven wear along a cylinder wall that makes the bore wider at one point than another, measured with a precision instrument and compared against the manufacturer's service limit.

The clearance between the two ends of a piston ring when fitted squarely in its bore, checked with a feeler gauge because too little gap causes ring breakage when the engine heats up.

The relationship stating that voltage equals current multiplied by resistance, used to calculate expected readings and interpret measurements when diagnosing an electrical circuit.

A test instrument that measures voltage, resistance and current, and often continuity, used to check circuits, sensors and actuators against specifications during electrical diagnosis.

A measurement of the voltage lost across a cable, connection or component while current flows, revealing high resistance such as corroded terminals or a poor earth.

Current drawn from the battery when the ignition is off and all accessories are shut down, which can flatten the battery if it exceeds the manufacturer's limit.

The voltage maintained across the battery by the charging system while the engine runs, typically about 13.5 to 14.5 volts, indicating whether the alternator and regulator are working.

A standardised alphanumeric code stored by the engine control unit when it detects a fault, read with a scan tool to guide diagnosis of sensors, circuits and emissions systems.

A device that connects to the vehicle's diagnostic socket to read fault codes, view live sensor data and clear codes after a repair has been verified.

A braking arrangement in which pedal force is transmitted through incompressible fluid in sealed lines to wheel cylinders or calipers, multiplying force at the wheels.

The process of removing trapped air from hydraulic brake lines by opening bleed screws and expelling fluid until a bubble-free flow is achieved, restoring a firm pedal.

A hygroscopic hydraulic fluid with a specified boiling point that transmits pressure in the braking system; absorbed moisture lowers its boiling point and it must be replaced at intervals.

The smallest thickness a brake disc may reach before replacement, measured with a caliper or micrometer and compared with markings on the disc or the manufacturer's specification.

A feature that warns of worn pads, either a metal tab that contacts the disc and squeals or a sensor that triggers a dashboard warning light.

Adjustment of camber, caster and toe angles so the wheels sit correctly relative to the vehicle and road, preventing uneven tyre wear and poor straight-line stability.

Correction of uneven mass distribution around a wheel and tyre assembly by adding weights, which prevents vibration at speed and reduces bearing and suspension wear.

A ball-jointed link between the steering rack or box and the wheel hub that transmits steering movement and provides a point for adjusting toe setting.

A hydraulic damper that controls spring oscillation after the wheels meet a bump, keeping the tyre in contact with the road and limiting body movement.

The hydraulic oil used in a power-assisted steering system to transmit pressure from the pump to the rack or box, reducing the effort needed to turn the wheel.

The driven disc in a manual transmission that is clamped between the flywheel and pressure plate, transmitting engine torque while allowing smooth take-up and disengagement.

The small amount of pedal or linkage movement before the release bearing begins to act, which must be within specification to prevent slipping or incomplete disengagement.

A fluid coupling in an automatic transmission that multiplies engine torque at low speed and allows the vehicle to stop in gear without stalling the engine.

Lubricating and hydraulic oil used in a gearbox or automatic transmission to reduce wear, transfer pressure and assist cooling; level and condition are checked during service.

A temperature-operated valve in the cooling system that stays closed while the engine warms and then opens to allow coolant flow through the radiator, maintaining normal operating temperature.

A mixture of water and antifreeze/corrosion inhibitor that carries heat from the engine to the radiator, raises the boiling point and lowers the freezing point.

A cap that holds the cooling system under pressure to raise the coolant boiling point and contains a valve that releases pressure or admits air as the system heats and cools.

A dashboard lamp that illuminates when engine oil pressure falls below a safe level, warning of possible pump failure, low oil level or a blocked oil passage.

A measure of an oil's resistance to flow at given temperatures, shown by a grade such as 5W-30, which must match the manufacturer's recommendation for the operating conditions.

A replaceable element that removes metal particles, sludge and other contaminants from engine oil before it reaches bearings and other moving parts.

An exhaust component containing a catalyst that converts harmful gases such as carbon monoxide, hydrocarbons and nitrogen oxides into less harmful substances before they leave the vehicle.

An emissions control system that routes crankcase blow-by gases back into the intake to be burned, preventing them from escaping to the atmosphere and reducing oil contamination.

An emissions control system that returns a measured portion of exhaust gas to the intake, lowering combustion temperature and reducing nitrogen oxide formation.

A structured safety check of a vehicle against legal requirements covering brakes, steering, suspension, tyres, lights, body structure and emissions, with results recorded on a certificate or report.

The height of the tread blocks measured in the main grooves, which must remain above the legal minimum to maintain grip and resist aquaplaning on wet roads.

A written or electronic record of a vehicle's booking that lists customer concerns, authorised work, parts used and labour time, forming the basis for the invoice and service history.

The customer's own words describing a symptom, recorded accurately at reception so the technician can reproduce and diagnose the fault rather than relying on a guessed interpretation.

The customer's documented approval of quoted work and cost before repairs proceed, protecting both parties and allowing extra work only after further consent is obtained.

A workshop unit that circulates solvent or aqueous cleaning fluid to remove grease from components, requiring correct fluid disposal and safe handling under hazardous chemical rules.