CDL Air Brakes TestAir Brake System PartsEasy
A driver is performing a pre-trip inspection on a commercial vehicle equipped with an Anti-lock Braking System (ABS). After starting the engine, the ABS indicator light comes on and then goes out. What does this typically indicate?
- AThe ABS is performing a self-test and is functioning correctly.
- BThe brake fluid level is critically low, affecting ABS performance.
- CThe vehicle's air pressure is too low for the ABS to operate.
- DA fault has been detected in the ABS requiring immediate service.
Show answer & explanationAnswer & explanation
Correct answer: A. The ABS is performing a self-test and is functioning correctly.
When an ABS indicator light comes on briefly after starting the engine and then goes out, it's a normal self-test sequence. This indicates that the ABS computer has checked its components and found them to be in proper working order.
Why the other options are wrong
- B. Commercial vehicles with air brakes do not use brake fluid for service brakes; this is irrelevant to an air brake ABS.
- C. ABS operates on the air brake system, but the light itself indicates an ABS component check, not directly air pressure levels.
- D. If a fault were detected, the light would typically stay on.
ABS Indicator Light Self-Test
A diagnostic sequence performed by the Anti-lock Braking System (ABS) computer upon vehicle start-up, indicated by the ABS light illuminating briefly and then turning off.
- Normal operation: Light comes on, then goes off.
- Light staying on indicates a fault.
- Confirms ABS system is operational.
Memory trick: Light On, Light Off = All Good, Boss.