SVP Light Vehicle Mechanic flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Wheel chock placement

Wheel chocks are placed against the wheels that remain on the ground, on both the front and rear sides of each chocked wheel, before a vehicle is lifted.

Hydrogen charging hazard

Charging a lead-acid battery can release hydrogen gas, which is explosive at concentrations of about 4% to 75% in air, so the charging area must be ventilated.

Battery disconnect order

When removing a battery, disconnect the negative terminal first; when installing it, connect the negative terminal last to reduce short-circuit risk from tools.

Torque formula

Torque equals force multiplied by perpendicular distance from the pivot; the metric unit is the newton metre, and 1 N·m equals about 0.7376 lbf·ft.

Micrometer reading

Read the barrel scale, then add the thimble scale multiplied by the least count; a typical metric micrometer thimble reads to 0.01 mm.

Impact socket use

Impact sockets are made softer and thicker than chrome hand sockets so they resist shock; chrome sockets can crack or shatter when used with impact tools.

Compression ratio formula

Compression ratio equals swept volume plus clearance volume, divided by clearance volume; it compares total cylinder volume to combustion chamber volume.

Torque-to-yield bolts

Torque-to-yield bolts are tightened to a specified torque and then an additional angle; they stretch permanently and must be replaced rather than reused.

Ring end gap

Piston ring end gap is measured with a feeler gauge after squaring the ring in its cylinder bore; too small a gap can cause ring butting and breakage.

Crankshaft position sensor

The crankshaft position sensor reports engine speed and crankshaft position to the ECU, which uses the signal for ignition timing and fuel injection.

Positive fuel trim

Positive fuel trim means the engine control unit is adding fuel because the measured mixture is lean; negative fuel trim means it is removing fuel from a rich mixture.

Knock sensor function

A knock sensor detects abnormal combustion vibration and sends a signal to the ECU, which retards ignition timing to reduce detonation and protect the engine.

Lambda value meaning

Lambda equals actual air-fuel ratio divided by stoichiometric ratio; lambda above 1 is lean, below 1 is rich, and 1 is stoichiometric.

EVAP purge valve

The EVAP purge valve controls flow of fuel vapour stored in the charcoal canister into the intake manifold, where it is burned during normal combustion.

EGR system purpose

Exhaust gas recirculation routes a small amount of exhaust into the intake, lowering peak combustion temperature and reducing nitrogen oxide emissions.

Ohm's law

Ohm's law states voltage equals current multiplied by resistance; power equals voltage multiplied by current, or current squared multiplied by resistance.

Parasitic draw test

Parasitic draw is measured with an ammeter in series with the battery after modules sleep; many vehicles should draw less than about 50 milliamps.

CAN bus termination

A CAN bus uses a twisted pair with two 120-ohm terminating resistors, one at each end, giving about 60 ohms measured across the bus.

Gear ratio definition

Gear ratio is driven gear teeth divided by drive gear teeth; a numerically higher ratio multiplies torque more and reduces output speed.

Torque converter stall

At stall the turbine is stationary while the engine turns the impeller; the torque converter multiplies engine torque before the vehicle begins moving.

Differential function

The differential allows the driven wheels to rotate at different speeds during turns while transmitting drive, and the final drive ratio multiplies torque.

Hydraulic pressure formula

Hydraulic pressure equals force divided by piston area; a larger output piston area produces greater force for the same system pressure.

Brake fluid hygroscopicity

DOT 3 and DOT 4 glycol brake fluids absorb moisture from the air, which lowers their boiling point and can cause vapour lock under hard braking.

ABS wheel speed sensors

ABS wheel speed sensors report each wheel's rotational speed; the control module modulates brake pressure to prevent wheel lock and maintain steering control.

Camber angle

Camber is the inward or outward tilt of the top of the wheel viewed from the front; negative camber means the top tilts inward.

Caster angle effect

Caster is the forward or backward tilt of the steering axis; positive caster improves straight-line stability and steering self-centering.

Air conditioning cycle

The A/C cycle uses a compressor, condenser, expansion device, and evaporator to move heat from the cabin to outside air by changing refrigerant pressure and phase.

Refrigerant phase change

Refrigerant absorbs heat when it evaporates at low pressure and releases heat when it condenses at high pressure; this phase change transfers heat.

DTC prefix letters

The first character of a diagnostic trouble code identifies the system: P is powertrain, C is chassis, B is body, and U is network communication.

Freeze frame data

Freeze frame data records operating conditions such as speed, load, and temperature at the moment a diagnostic trouble code is set.

Tire tread minimum

Many regions set a legal minimum tire tread depth of 1.6 millimetres; worn tires reduce wet grip and increase hydroplaning risk.

Oil viscosity rating

In a multigrade oil such as 5W-30, the first number indicates cold-flow performance and the second number indicates viscosity at operating temperature.