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). They notice that after turning the ignition key to the 'on' position, the amber ABS indicator light illuminates for a few seconds and then turns off. What does this indicate?
- AA fault in the ABS system requiring immediate service.
- BThe vehicle's air pressure is too low for the ABS to operate.
- CThe ABS system has been manually deactivated by the driver.
- DThe ABS system is performing a self-test and is functioning correctly.
Show answer & explanationAnswer & explanation
Correct answer: D. The ABS system is performing a self-test and is functioning correctly.
The illumination of the ABS light for a few seconds upon ignition and its subsequent turning off is a normal self-test sequence. It indicates that the ABS system is operational and has not detected any faults.
Why the other options are wrong
- A. A fault would typically cause the light to remain on or flash continuously.
- B. Low air pressure would trigger the low air warning, not necessarily the ABS light in this manner.
- C. ABS systems are rarely manually deactivated, and if so, the light would likely remain on to indicate deactivation.
ABS Indicator Light Self-Test
The routine sequence where the Anti-lock Braking System (ABS) indicator light illuminates briefly upon vehicle start-up and then extinguishes, signifying that the ABS system is performing a self-diagnostic check and is operating correctly.
- Normal operation for most modern ABS systems.
- Light staying on indicates a fault.
- Ensures system readiness for emergency braking.
Memory trick: Light On, Light Off? ABS is A-OK!