Vehicle Maintenance, Diagnostics and Servicing
This domain tests planned maintenance, fault diagnosis, and servicing. You should know preventive versus breakdown maintenance, service schedules, OBD-II fault codes, and a logical diagnostic sequence.
Core concepts
- Preventive maintenance follows time or distance intervals; corrective maintenance repairs a known fault; predictive maintenance uses condition monitoring.
- A service includes fluid checks, filter replacement, tyre inspection, brake inspection, battery testing, and road test.
- OBD-II stores diagnostic trouble codes (DTCs) and freeze-frame data. Record codes before clearing them.
- Diagnosis should follow: verify the complaint, check basics, scan for codes, test the circuit or component, then repair and confirm.
- A road test confirms repair under load and speed; it must be done safely and legally.
Worked example
A car battery goes flat after standing for a week. A clamp meter shows 50 mA parasitic drain. Over 24 hours that is 0.05 A × 24 h = 1.2 Ah; over seven days it is about 8.4 Ah. If the battery is healthy but small, this drain can prevent starting. The reasoning is to convert current and time into ampere-hours, compare with battery capacity, then isolate the circuit causing the drain.
Traps that cost marks
- Clearing DTCs before recording freeze-frame data.
- Replacing parts without testing the circuit.
- Checking only the battery when the complaint is slow cranking; inspect cables and earths.
- Ignoring tyre pressures and fluid levels during a road test.
- Treating a warning lamp as a confirmed component failure.