EV Maintenance, Diagnosis and Troubleshooting
What this domain covers
This domain tests scheduled maintenance, fault diagnosis and repair logic for EVs, including the 12 V system, HV insulation, DTCs and road-test checks.
Core rules and concepts
- EV maintenance: no engine oil or spark plugs; check battery coolant, brake fluid, tyres, suspension, steering, HV connectors, seals, cabin filter and software updates.
- 12 V auxiliary battery: powers controllers, lights and contactors; a weak 12 V battery can mimic major HV faults.
- Diagnosis sequence: verify the complaint, scan DTCs, check live data, inspect the circuit, test the component, repair and confirm.
- Insulation testing: use a suitable insulation tester on an isolated circuit; low insulation resistance means a leak path.
- Brakes: regen reduces friction-brake use, so inspect for corrosion and seizing.
- Road test: check noise, vibration, power delivery, regen and warning lamps.
Worked example
An EV does not start and the dashboard is dead. Reasoning: start with the 12 V battery, not the HV pack. Check voltage, terminals and fuses. If 12 V is low, charge or replace it, then recheck. Only after the low-voltage system is healthy should you scan for HV faults. This order avoids unnecessary HV work.
Traps that cost marks
Do not replace the HV battery on a symptom alone. Do not ignore the 12 V battery. Do not clear DTCs before recording them. Do not probe HV connectors with a standard multimeter. Do not assume regen means the friction brakes need no service. Do not return a vehicle without confirming the repair and documenting the test.