SKM Motor Vehicle Mechanic L2 flashcards

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

Hierarchy of control

Ranking of risk controls from most to least effective: elimination, substitution, engineering controls, administrative controls and PPE. PPE is the last line of defence, not the first choice.

Carbon monoxide hazard

Odourless gas from petrol engines that binds haemoglobin far more readily than oxygen. Never run an engine in an enclosed bay without extraction, because exposure can be fatal without warning.

Micrometer least count

Pitch of the screw thread divided by the number of thimble divisions. A 0.5 mm pitch with 50 divisions reads to 0.01 mm, the smallest change the instrument can display.

Vernier caliper reading

Main scale value plus the coinciding vernier division multiplied by the least count. A 0.02 mm vernier with the seventh line coinciding adds 0.14 mm to the main scale.

Compression ratio formula

Swept volume plus clearance volume, divided by clearance volume. A 500 cc swept volume with 50 cc clearance gives a ratio of 11 to 1.

Four-stroke cycle order

Intake, compression, power and exhaust. The crankshaft turns twice, or 720 degrees, for each complete cycle, so each cylinder fires once every two revolutions.

Ohm's law and power

Voltage equals current multiplied by resistance, and power equals voltage multiplied by current. A 12 V supply across 6 ohms draws 2 A and dissipates 24 W.

CAN bus termination

Two 120 ohm terminating resistors in parallel give about 60 ohms measured across the bus with power off. A different reading indicates a wiring or termination fault.

Overall gear ratio

Gearbox ratio multiplied by final drive ratio. It shows how many engine revolutions are needed for one wheel revolution and determines torque multiplication and road speed.

Wheel alignment angles

Camber is vertical wheel tilt, caster is steering-axis tilt affecting self-centring, and toe is the difference in track between front and rear of the wheels.

Brake fluid hygroscopy

DOT 4 fluid absorbs moisture from the air, which lowers its boiling point and can cause fade. Replacement is typically every two years regardless of mileage.

Spongy brake pedal cause

Air in the hydraulic system is the usual cause, because gas compresses while fluid does not. Bleed the system in the manufacturer's sequence and recheck pedal feel.

Diagnostic trouble codes

Codes describe symptoms, not causes. A lean code can come from a vacuum leak, low fuel pressure or a faulty sensor, so confirm with live data before replacing parts.

Fuel trim interpretation

Long-term fuel trim above about plus 10 percent indicates a lean condition, while negative trim indicates rich running. Trims show how much the ECU is correcting.

Tyre tread depth minimum

The legal minimum is 1.6 mm across the central three-quarters of the tread. Replacement earlier than this improves wet grip and reduces aquaplaning risk.

Tyre pressure checking

Pressures are checked cold, before driving heats the tyre. A warm tyre reads higher and must not be bled down to the cold figure, or it will be under-inflated.

Job card contents

Vehicle details, VIN, odometer, customer complaint, authorised work, parts used, labour time and technician signature. It is the record of what was agreed and done.

Waste segregation

Used oil, filters, coolant, brake fluid, solvents, batteries and tyres each follow separate licensed disposal routes. Mixing streams makes recycling impossible and may be illegal.

Torque-to-yield bolts

Head bolts tightened to a torque then turned a specified angle stretch permanently and must be replaced, not reused. Reuse risks loss of clamping force and head gasket failure.

Head gasket failure signs

Coolant loss without an external leak, white exhaust smoke, bubbles in the expansion tank and oil mixed with coolant. A compression or leak-down test confirms the diagnosis.

Brake bleeding order

Usually furthest from the master cylinder first, following the manufacturer's sequence. Keep the reservoir topped up throughout to prevent air being drawn into the system.

Disc thickness variation

Uneven disc thickness causes pulsation through the brake pedal. Measure with a micrometer at several points around the disc and compare with the wear limit.

Differential function

Allows the driven wheels to turn at different speeds in a turn. Noise or locking may indicate incorrect oil, worn gears or a failed limited-slip unit.

Steering free play

Measured at the steering wheel rim with the wheels straight ahead. Excessive play indicates worn tie rods, a worn rack or a loose steering column joint.

Voltage drop testing

Measures voltage lost across a circuit under load. More than about 0.5 V on a main feed indicates high resistance that an ohmmeter alone may not reveal.

Parasitic drain test

Measures current with everything off and modules asleep. A reading above the manufacturer's limit indicates a fault that discharges the battery overnight.

Leak-down test

Pressurises the cylinder and shows where air escapes: intake, exhaust, crankcase or coolant. It distinguishes ring, valve and head gasket faults better than compression alone.

Smoke testing intake

Introduces smoke into the intake to reveal vacuum leaks that visual inspection misses. Leaks cause lean running, rough idle and fuel trim errors.

Belt and hose inspection

Belts showing cracks, glazing or fraying need replacement. Hoses that feel hard, cracked or swollen under squeeze should be replaced before they fail.

Service indicator reset

Part of the service procedure and must be recorded on the job card. Leaving it set can mislead the customer about when the next service is due.

Safety data sheets

Provide hazard, handling, storage and first-aid information for workshop chemicals. They must be accessible to staff and kept up to date for every product used.

Customer handover

Explains what was done, what was found, what may need attention next and the warranty terms. Recording the customer's decision protects both parties.