Vehicle Inspection, Testing and Fault Diagnosis
Domain focus
Vehicle Inspection, Testing and Fault Diagnosis tests roadworthiness checks, test equipment, and a logical diagnostic sequence. It emphasizes measured evidence rather than guesswork.
Core rules
- Inspection covers brakes, steering, suspension, tyres, lights, emissions, and structural condition.
- Brake roller testers measure individual wheel force; imbalance is compared with the higher or specified reference force.
- Headlamp aim is checked against a beam setter; tyre pressure and load affect aim and brake results.
- Emission tests use gas analysers for petrol and smoke meters for diesel, at specified idle and fast-idle conditions.
- Diagnosis sequence: verify complaint, gather data, narrow the system, test, repair, and confirm.
Worked example
A service-brake test gives 2.4 kN on the left and 1.8 kN on the right. Difference = 0.6 kN. Using the higher force as reference, imbalance = 0.6 ÷ 2.4 × 100 = 25%. If the limit is 30%, the vehicle passes, but the result is close enough to justify checking a sticking caliper, contaminated lining, or restricted hose. Re-testing after repair must reproduce the result within specification.
Traps
Testing cold brakes, ignoring tyre pressure, and comparing left and right without confirming the reference method. Headlamp aim can be misread if the vehicle is not on level ground. A scan-tool code is not a diagnosis until the circuit and mechanical condition are tested.