Antilock Braking Systems (ABS) and Air Brake System Malfunctions
Domain 7 tests ABS operation and common air brake malfunctions. The exam asks what ABS does, what a dash lamp means, and how to respond to low pressure, leaks, and component failures.
ABS and malfunctions
- ABS prevents wheel lock and helps steering control; it does not always shorten stopping distance.
- Yellow ABS lamp: if it stays on, ABS is disabled; normal service brakes remain.
- With ABS, press and hold the brake in an emergency; do not pump.
- Trailer ABS lamp may be separate; check it during inspection.
- Low-pressure warning, compressor failure, governor failure, leaks, frozen lines, and brake fade are system faults.
- Red brake warning lamp indicates a brake system problem; stop and investigate.
Worked example
After start-up, the yellow ABS lamp stays on. Reasoning: ABS may be disabled, but the service brakes still work. The driver should not pump the brakes or assume ABS will operate; the vehicle should be checked, and driving should be cautious.
Traps that cost marks
Thinking ABS always shortens stops; confusing the ABS lamp with the red brake warning; pumping ABS; ignoring a low-pressure warning because the vehicle still moves; treating a leak as normal.