CDL Air Brakes TestAir Brake System PartsEasy
A driver is inspecting a vehicle equipped with an anti-lock braking system (ABS). After starting the engine, the yellow ABS indicator light illuminates on the dashboard, then goes out after a few seconds. What does this indicate about the ABS?
- AThe ABS controller has detected a low air pressure condition.
- BThe vehicle's speed sensors are malfunctioning.
- CThe ABS has completed its self-test and is functioning correctly.
- DThe ABS is faulty and requires immediate repair.
Show answer & explanationAnswer & explanation
Correct answer: C. The ABS has completed its self-test and is functioning correctly.
A normal ABS self-test sequence involves the indicator light illuminating briefly upon engine start, and then turning off. This indicates that the system has checked itself and found no faults, confirming it is operational.
Why the other options are wrong
- A. The ABS light indicates ABS system status, not general low air pressure (which has its own warning).
- B. Malfunctioning speed sensors would likely cause the ABS light to remain on.
- D. If the ABS were faulty, the light would typically stay on or flash.
ABS Indicator Light Self-Test
The yellow ABS indicator light illuminates briefly upon vehicle startup and then extinguishes, signaling that the Anti-lock Braking System has successfully completed its self-diagnostic check.
- Brief illumination at start is normal.
- Extinguishing indicates no faults detected.
- Staying on means a malfunction.
Memory trick: Light on, then Light off, means ABS is on the job.