Diagnosis, servicing, repair and quality control
This domain tests systematic fault-finding, scheduled servicing and the checks that prove a repair is safe. It rewards evidence and documentation, not guesswork.
Core rules
- Diagnosis sequence: confirm the complaint, interview the rider, check obvious causes, test in a logical order, repair, verify by road test.
- Use the three essentials for a petrol engine: good spark, correct fuel mixture, adequate compression. Test each before replacing parts.
- Read stored fault codes before clearing them; record freeze-frame data. Do not replace a sensor because of a code without testing its circuit.
- Servicing follows the manufacturer's schedule: oil and filter, air filter, valve clearance, brake fluid, chain, tyre pressures, fasteners.
- Quality control: torque check, fluid levels, brake feel, throttle return, no leaks, lights and horn, road test, then sign-off.
- Document measurements and parts fitted so the next technician can trace the work.
Worked example
A motorcycle cranks but will not start. Reasoning: check battery voltage while cranking, then spark at the plug, then fuel at the injector or carburettor, then compression. If spark is strong and fuel is present but compression is 5 bar against a 10 bar specification, the fault is mechanical: valve clearance, timing or piston rings. A leak-down test locates it by listening at the intake, exhaust and oil filler.
Traps
Swapping parts without testing; clearing codes before reading them; skipping the road test; ignoring a customer's description of when the fault occurs; returning a bike with a loose axle nut.