Punjab PSEB Sr. Sec. NSQF Automotive (Four Wheel Service Technician) key terms

The set of safety items worn while working on vehicles, including safety goggles, gloves, steel-toe boots and hearing protection, chosen to reduce injury from chemicals, sharp edges, hot parts and flying debris.

A standard document supplied with a chemical product that lists its hazards, safe handling, storage, first-aid measures, spill response and required protective equipment before the product is used in the workshop.

A procedure in which an energy source is isolated, locked and tagged so machinery or a vehicle cannot be started or release stored energy while a technician services it, protecting people from sudden movement or electrical shock.

Separating workshop waste such as used oil, coolant, batteries, tyres and metal scrap into labelled containers so each stream can be recycled or disposed of lawfully without contaminating soil or water.

Collecting drained engine, gearbox and hydraulic oil in dedicated containers and handing it to an authorised recycler, because a single litre can pollute a very large volume of groundwater and the oil can be re-refined.

A ventilation system that captures exhaust gas, paint mist, welding smoke or solvent vapour at its source and moves it outdoors or through filters, keeping airborne concentrations in the workshop below harmful levels.

The three conditions needed for combustion: fuel, oxygen and an ignition source. Removing any one of the three extinguishes or prevents a fire, which guides safe fuel handling and extinguisher selection.

The classification of fires by fuel type: A for solids, B for flammable liquids, C for gases, D for metals and electrical fires, each requiring a suitable extinguisher such as water, foam, dry powder or CO2.

An uncontrolled self-heating chain reaction inside a battery cell, especially lithium-ion, that can release toxic gas, ignite or explode. It follows overcharging, internal short circuits, physical damage or overheating.

Precautions for working on hybrid and electric vehicle systems above about 60 volts DC, including approved insulated gloves, insulated tools, voltage verification before contact and isolating the service plug.

Disconnecting or removing the battery service plug or terminal, and waiting for capacitors to discharge, so high-voltage circuits are de-energised before any repair work begins on hybrid or electric vehicles.

A precision measuring instrument with a calibrated screw and thimble, used to measure outside diameters, thickness and wear on parts such as crankshaft journals and brake discs, typically reading to 0.01 mm.

A measuring tool with a fixed main scale and a sliding vernier scale that reads outside, inside, depth and step dimensions, commonly used in workshops to measure to 0.02 mm or 0.05 mm.

A dial or digital instrument that measures the internal diameter of a cylinder at several heights and directions, revealing taper, out-of-round and wear before deciding on reboring or honing.

A spring-loaded gauge with expanding contacts that is set inside a bore and then measured with a micrometer, giving an indirect but accurate reading of internal diameter where a bore gauge is unavailable.

A set of thin, marked steel blades of graduated thickness used to measure small clearances such as valve lash, spark plug gaps, brake pad gaps and contact breaker points by finding the blade that just fits.

A wrench that applies a preset or indicated tightening torque to a fastener, ensuring bolts such as cylinder head and wheel nuts are tightened to specification and evenly, preventing distortion, loosening or thread damage.

The specified order in which multiple fasteners, such as cylinder head bolts, are tightened, usually in a spiral from the centre outwards and in stages, so the clamped part is loaded evenly without warping.

A fastener tightened until it stretches beyond its elastic limit into the plastic range, giving a calculated clamp load. It must usually be replaced after removal and is tightened by angle rather than torque alone.

The operating cycle of most vehicle engines: intake, compression, power and exhaust, each completed in two crankshaft revolutions. The piston performs four strokes while the valves open and close in sequence.

The ratio of cylinder volume with the piston at bottom dead centre to the volume at top dead centre. Higher ratios generally raise efficiency and power but demand higher-octane fuel to avoid detonation.

The small designed gap between the valve stem and rocker or cam, allowing for thermal expansion. Too little causes valve leakage and burning; too much causes noise, reduced lift and wear.

The exact crankshaft positions at which intake and exhaust valves open and close, determined by camshaft profile and timing marks. Incorrect timing reduces power and can cause piston-to-valve contact.

Abnormal combustion in which the end gas ignites spontaneously ahead of the flame front, producing a sharp knocking sound, high cylinder pressure and possible piston damage, often caused by low-octane fuel, overheating or over-advanced timing.

A toothed belt that synchronises the rotation of the crankshaft and camshaft so valves open at the correct moment. It usually requires replacement at a specified interval because failure can destroy the engine.

A metal chain, guided by tensioners and rails, that drives the camshaft from the crankshaft. It is generally more durable than a belt but can stretch, become noisy and jump a tooth if neglected.

A coupling between engine and gearbox that transmits drive through pressed friction surfaces. The driver disengages it with the pedal to start moving or change gear smoothly.

The small clearance at the clutch pedal or release mechanism before the release bearing contacts the pressure plate. Correct play prevents slipping and premature wear; excess play prevents full disengagement.

A bearing that pushes against the rotating pressure plate fingers when the clutch pedal is pressed, allowing the clutch to disengage. It is a common wear item that produces noise when worn.

A stepped-ratio transmission in which the driver selects gears through a shift mechanism, using synchromesh to match speeds. It provides multiple torque and speed combinations from the engine.

A cone-and-sleeve mechanism inside a manual gearbox that brings the gear and shaft to matching speed before engagement, preventing gear clash and allowing smooth shifting without double declutching.

A gear set that lets the two driven wheels turn at different speeds while cornering, while still delivering torque to both. It works with the final drive in rear- or front-wheel-drive layouts.

An electronic system that monitors wheel speed and modulates brake pressure to prevent wheel lock-up during hard braking, helping the driver retain steering control on slippery surfaces.

A sensor at each wheel, usually magnetic or Hall-effect, that reports rotational speed to the ABS and stability control units. A faulty sensor disables ABS and often triggers a warning lamp.

A hygroscopic hydraulic fluid that transmits pedal force to the brakes. It must have a high boiling point and be changed periodically, because absorbed moisture lowers the boiling point and causes vapour lock.

A temporary loss of braking efficiency caused by overheating of pads, discs or fluid during repeated heavy braking, reducing friction or creating vapour in the hydraulic system until the brakes cool.

The rotating metal plate clamped by the brake pads in a disc brake. It is checked for thickness, runout, scoring and cracks, because wear or distortion causes vibration and poor braking.

Adjustment of suspension angles, mainly camber, caster and toe, so the wheels point in the intended directions relative to the vehicle and road, preventing uneven tyre wear and steering pull.

Adding correct weights to a wheel rim so its mass is distributed evenly about the axle, eliminating vibration at speed caused by heavy spots in the tyre, tube or rim.

The height of the rubber pattern above the tyre grooves, measured in millimetres. It must stay above the legal minimum to disperse water and maintain grip; worn tread increases aquaplaning risk.

Periodically moving wheels between positions on the vehicle so that tread wears more evenly, compensating for the different loads and forces at front, rear, drive and steered axles.

A hydraulic damper that converts spring oscillation into heat, controlling body movement after bumps and keeping the tyres in contact with the road for grip and stability.

A front suspension design combining a coil spring, damper and wheel-locating strut in one unit, saving space and weight. Worn strut mounts or bearings cause noise and steering memory.

A steering system in which a pinion on the steering column drives a toothed rack, converting rotation into sideways movement that pushes the tie rods and turns the front wheels.

A system using hydraulic pressure or an electric motor to assist steering effort. Faults such as low fluid, a slipping belt or a failed motor increase effort and may trigger a warning lamp.

The alternator, regulator and battery circuit that generates electrical power while the engine runs and keeps the battery charged. Low output causes dim lights and a flat battery.

The amount of charge a battery can deliver, stated in ampere-hours, together with its cold cranking rating. It determines starting ability and how long electrical loads can run with the engine off.

A high-current electric motor that engages a pinion with the engine flywheel ring gear to crank the engine until it fires, then disengages automatically via the solenoid or drive.

A code stored by an electronic control unit when it detects an out-of-range signal or failed self-test, guiding the technician to the affected circuit or component through a scan tool.

The vehicle's self-monitoring system and standardised connector that give access to emission-related fault codes, live sensor data and readiness monitors for testing and repair.

A sensor in the exhaust that measures oxygen content and reports to the engine control unit, which adjusts fuel delivery to maintain the correct air-fuel ratio and protect the catalytic converter.

An exhaust device containing precious-metal catalysts that convert carbon monoxide, hydrocarbons and nitrogen oxides into less harmful gases. It requires unleaded fuel and correct mixture to work properly.

A colourless, odourless and poisonous gas produced by incomplete combustion. It is measured in exhaust gas testing and must never accumulate in a closed workshop because it binds haemoglobin.

A system that routes a small portion of exhaust gas back into the intake to lower combustion temperature, reducing nitrogen oxide emissions. Blocked passages cause rough running and fault codes.

A device in diesel exhaust that traps soot particles and periodically burns them off at high temperature in a process called regeneration. Short journeys can clog it and trigger a warning.

A conversion set with high-pressure cylinder, regulator, gas injectors or mixer and safety valves that lets a petrol engine run on compressed natural gas, requiring approved installation and periodic leak testing.

The manufacturer's table of service tasks at specified time or distance intervals, such as oil and filter changes, inspections and adjustments, which keeps the vehicle safe, reliable and within warranty.

A checklist performed on a new or repaired vehicle before handover, covering fluids, tyre pressures, lights, battery, road test and removal of transport protection, to confirm it is fit for the customer.

Verifying engine oil, coolant, brake fluid, power steering fluid, washer fluid and battery electrolyte against marks on a dipstick or reservoir, noting colour and smell as clues to internal faults.

A controlled drive after repair or during diagnosis to confirm symptoms, assess braking, steering, suspension, transmission and engine behaviour, and verify that the fault has been corrected.