Vehicle Diagnostics, Servicing and Maintenance
What this domain tests
A logical diagnostic process, OBD fault codes, scan-tool data, servicing schedules and preventive maintenance. The exam favours fault-isolation order and interpretation of live data.
Core rules and concepts
- Diagnostic order: verify the complaint, check basics, retrieve codes and freeze frame, test the circuit or component, repair, then confirm.
- DTC prefixes: P powertrain, C chassis, B body, U network. The code identifies a circuit or system, not automatically the failed part.
- Freeze frame records operating conditions when the fault set; record it before clearing codes.
- Live data and oscilloscope traces show what the sensor is doing; a scan tool is a measuring aid, not a repair.
- Basic checks still matter: fuel pressure, spark, air intake leaks, compression, battery voltage and grounds.
- Servicing includes oil and filter, fluid levels, tyre rotation and pressures, brake inspection, suspension check and road test.
- Complete the job card and record measurements so the next technician can trace the work.
Worked example
P0301 means cylinder 1 misfire. Record freeze frame, then swap the ignition coil from cylinder 1 to cylinder 2. If the code changes to P0302, the coil is faulty. If P0301 remains, test the injector, spark plug and compression for cylinder 1. Reason: moving a known component isolates whether the fault follows the part.
Traps that cost marks
Clearing codes before reading freeze frame; replacing a sensor because the code names its circuit; ignoring vacuum leaks; skipping the road test; not checking battery voltage before diagnosing electronics.