Vehicle Inspection, Periodic Maintenance and Diagnosis
This domain covers scheduled servicing, pre-delivery inspection, road testing, OBD diagnosis and repair verification. The exam tests a logical diagnostic sequence and the ability to interpret freeze-frame and live data rather than guess parts.
Core rules
- Periodic service includes engine oil and filter, air filter, coolant, brake fluid, belts, brake pads, tyre pressures and tread, lights, battery and suspension checks. Follow the manufacturer interval and the severe-use schedule for dusty or short-trip operation.
- PDI checks include fluid levels, tyre pressures, wheel nut torque, battery charge, function of lights and controls, and removal of transport protection. Record findings.
- OBD diagnosis: record the DTC and freeze frame before clearing. Use live data for fuel trims, sensor voltages, misfire counters and commanded vs actual values.
- Road test safely: check braking, steering, transmission shift quality, noises and warning lamps. Verify the repair by repeating the original complaint test and confirming no pending codes return.
- Five-gas analysis and compression or cylinder-leak testing support mechanical diagnosis when electronic data is inconclusive.
Worked example
A car sets P0300 random misfire. Freeze frame shows 1800 rpm and light load. Live data shows long-term fuel trim +18% on bank 1 and misfire counts on several cylinders. The technician checks for a vacuum leak and finds a split intake hose. Reasoning: a lean condition affects all cylinders on that bank; repairing the leak returns fuel trim toward zero and stops the misfire.
Traps
- Clearing DTCs before recording freeze frame and readiness status.
- Replacing parts without checking fuel trim, compression or ignition data.
- Ignoring a technical service bulletin for a known fault.
- Failing to repeat the road test and confirm the repair.