Vehicle technology, maintenance and defect recognition
Domain 5 tests daily checks, defect recognition and basic vehicle technology for heavy goods vehicles. You are expected to spot faults before they become roadside prohibitions, report them correctly and understand what systems such as ABS, EBS, SCR and retarders do.
Daily walk-around
Check tyres and wheel nuts, lights and reflectors, mirrors, windscreen and wipers, brake lines and air leaks, coupling and fifth-wheel jaws, trailer legs, curtains and doors, load security, AdBlue level, oil and coolant, and warning lamps. Test the brakes at low speed after moving off. Record defects; a defect that affects safety must be repaired before the vehicle is used. In Denmark, periodic roadworthiness testing ('syn') is separate from the daily check.
Tyres and brakes
Heavy vehicle tyres have a legal minimum tread depth in the central tread area; for a lorry this is generally 1.0 mm, while car tyres are 1.6 mm. Check pressures cold. Uneven wear tells a story: inner-edge wear on one front tyre suggests alignment; centre wear suggests overinflation; both shoulders suggest underinflation; cupping suggests suspension or damper problems. ABS prevents wheel lock but does not shorten every stopping distance. Air-brake systems need correct pressure; listen for leaks and check the test points.
Emissions and warning lamps
SCR uses AdBlue to reduce NOx; running out can derate the engine. A flashing DPF lamp may require a regeneration run, not a motorway race. A red warning lamp means stop safely and investigate; amber means proceed to a workshop or follow the handbook.
Worked example
A driver reports vibration at 80 km/h and a front tyre worn on the inner edge. Wheel balance would usually cause vibration, but inner-edge wear points to toe/alignment. The correct response is to report both symptoms, check tyre pressures and suspension play, and book alignment; simply replacing the tyre will repeat the wear. If a wheel bearing is also noisy, the vehicle should be stopped until assessed.
Traps
Ignoring an amber lamp; overfilling oil; using the wrong AdBlue; assuming ABS means you can brake later; and treating a tyre-pressure warning as a nuisance.