Red Seal Automotive key terms

A hand tool that measures and limits the twisting force applied to a fastener so it can be tightened to a manufacturer-specified value without being overstretched or damaged.

A bolt designed to be tightened until it stretches into its elastic range, producing clamping force; it usually must be replaced rather than reused after removal.

A standardized document that lists a chemical product's hazards, safe handling procedures, first-aid measures, and spill or fire response information for workers.

A safety procedure in which an energy source is physically locked and marked with a tag so equipment cannot be started while service work is being performed.

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

The ratio of the cylinder's total volume when the piston is at the bottom of its stroke to the volume remaining when it is at the top.

The small gap between the valve stem tip and the rocker arm or camshaft lobe that allows the valve to close fully as engine parts expand with heat.

A valve that bypasses exhaust gas around the turbine to limit boost pressure, protecting the engine from over-boost and detonation.

A valve that meters a small amount of exhaust gas back into the intake to lower combustion temperature and reduce nitrogen oxide emissions.

A test that pressurizes a cylinder with compressed air and measures the percentage leaking out, helping locate bad rings, valves, or head gasket.

A measurement of the voltage lost across a circuit while current flows; excessive drop indicates high resistance at a connection, cable, or component.

Current that continues to flow from the battery when the ignition is off and all accessories are shut down, often caused by a faulty module or relay.

A two-wire communication network that lets electronic control modules share data at high speed using digital messages rather than separate wires for every signal.

A digital control method that switches a circuit on and off rapidly; the ratio of on-time to total time determines the average voltage or current delivered.

A sensor that produces a voltage when a magnetic field passes through it, commonly used to detect wheel speed, crankshaft position, or camshaft position without mechanical contact.

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

A differential that limits the speed difference between the two driven wheels, sending torque to the wheel with more traction when one slips.

A joint that transmits power through a varying angle at constant rotational speed, commonly used at the ends of front-wheel-drive halfshafts.

A gearbox that splits engine power between the front and rear axles in a four-wheel-drive or all-wheel-drive vehicle, often offering high and low ranges.

The small amount of clearance between meshing gear teeth that allows lubricant to flow and prevents binding as gears expand and wear.

A pump that converts brake pedal force into hydraulic pressure, pushing brake fluid through lines to the wheel brakes.

A loss of braking force caused by overheating, which can boil brake fluid or reduce friction between pad and rotor during repeated hard stops.

An electronic system that rapidly modulates brake pressure at each wheel to prevent lockup and maintain steering control during hard braking.

A valve that limits hydraulic pressure to the rear brakes so they do not lock before the front brakes during hard stops.

The process of removing air from hydraulic brake lines by opening bleeder screws and forcing fluid through until no bubbles remain.

The inward or outward tilt of the top of a wheel viewed from the front, measured in degrees from vertical; it affects tire wear and handling.

The forward or rearward tilt of the steering axis viewed from the side; it affects straight-line stability and steering return.

The difference in distance between the front and rear of the tires on the same axle; toe-in means the fronts point toward each other.

The direction the rear axle points relative to the vehicle's centreline, determined by rear toe; it affects steering wheel position and tire wear.

A flexible socket-and-stud joint that connects the steering knuckle to the control arm while allowing suspension movement and steering rotation.

A fluid that absorbs heat when it evaporates and releases heat when it condenses, carrying heat out of the passenger compartment in an A/C system.

A heat exchanger mounted in front of the radiator that releases heat from high-pressure refrigerant gas so it condenses into a liquid.

A heat exchanger inside the cabin where low-pressure refrigerant absorbs heat from the air, cooling and dehumidifying it.

A fixed restriction that meters refrigerant flow into the evaporator, causing a pressure drop that lowers refrigerant temperature.

A thermostatic valve that regulates refrigerant flow into the evaporator by opening or closing in response to outlet temperature and pressure.

A vehicle body design in which the floor, pillars, and panels are welded together to form a single structural unit that supports the drivetrain and absorbs loads.

A section of the vehicle structure designed to deform and absorb energy in a collision, reducing forces transferred to the occupants.

An airbag and seat-belt system that deploys supplemental protection in a serious collision; it works with, not instead of, the seat belts.

An electronic module that controls body functions such as lights, locks, windows, wipers, and security, and communicates with other modules over the network.