Vehicle Maintenance, Fault Diagnosis and Repair
Vehicle Maintenance
Preventive maintenance
Vehicle maintenance keeps safety, reliability and emissions within specification. Candidates must know service schedules, fluid checks and replacement, filter changes, tyre inspection and rotation, brake inspection, battery care, lubrication, cooling-system service, and record keeping. Engine oil must meet the specified viscosity and service category; coolant must be the correct type to prevent corrosion and overheating. Tyre pressures are checked cold, and tread depth and uneven wear are recorded. Brake fluid absorbs moisture and should be renewed at the recommended interval. Battery terminals should be clean and tight, and the charging system checked if starting is slow.
Traps in questions
A frequent trap is treating severe-service schedules as if they were normal; dusty roads, short trips and heavy loads shorten intervals. Another is mixing coolant types or using plain water, which reduces boiling protection and promotes corrosion. Questions may test that tyre rotation promotes even wear but does not correct misalignment. Do not over-tighten wheel nuts or oil drain plugs; use the specified torque. Service records matter for warranty and fault history.
Rule of thumb
Check tyres, fluids, lights and brakes at every service; use the manufacturer's severe-service interval when operating conditions are harsh.
Worked example: a vehicle used on dusty roads and for short trips should follow the severe-service oil-change interval rather than the normal interval, because contamination and condensation accelerate oil degradation.
Fault Diagnosis and Repair
A logical diagnostic process
Fault diagnosis is a structured search for the root cause, not a guessing game. Candidates should use a repeatable sequence: verify the complaint, gather information, inspect, test, isolate the fault, repair, and confirm. Symptoms must be confirmed under the conditions described by the customer. Diagnostic trouble codes (DTCs) point to a circuit or system, not always to the failed component. Use compression and leak-down tests for mechanical faults, fuel-pressure and vacuum tests for intake and fuel faults, and oscilloscopes or multimeters for electrical signals. Intermittent faults require checking connectors, earths, and wiring movement.
Traps in questions
A common trap is replacing a sensor because its code appears, without testing the circuit. Another is confusing cause with effect: a vacuum leak can cause lean codes and misfire, but the leak is the cause. Questions may ask why a no-start diagnosis should check battery voltage and cranking speed first. Do not overlook the basics: fuel level, immobiliser, security system, and battery terminals. After repair, clear codes and road-test to confirm the fix.
Rule of thumb
Test, do not guess. If a fault is intermittent, reproduce it and wiggle-test wiring while watching live data.
Worked example: an engine cranks slowly and will not start. Check battery voltage while cranking; if it falls below about 9.6 V, test the battery, terminals and starter circuit before investigating ignition or fuel.