CDL Air Brakes TestDual Air Brake SystemsHard
A technician is performing a pre-trip inspection on a vehicle with a dual air brake system. They notice that the air pressure gauges show normal operating pressure (120 psi) for both primary and secondary systems, but the low air pressure warning light remains illuminated. What should be the technician's next step?
- AContinue the pre-trip, as the gauges show normal pressure.
- BImmediately replace the air compressor.
- CBleed air from the system to see if the warning light goes off.
- DCheck the wiring and sensor for the low air pressure warning system.
Show answer & explanationAnswer & explanation
Correct answer: D. Check the wiring and sensor for the low air pressure warning system.
If the air pressure gauges correctly indicate normal operating pressure (120 psi) but the low air pressure warning light is still on, it suggests an electrical fault with the warning system itself, not an actual low air pressure condition. The most logical next step is to inspect the warning light's wiring and pressure sensor.
Why the other options are wrong
- A. An illuminated warning light, even if seemingly false, indicates a malfunction that must be addressed before operation, as it could mask a real problem later or lead to a violation.
- B. The compressor is likely working correctly since both systems are at normal pressure, so replacing it would be premature and incorrect.
- C. Bleeding air would intentionally lower pressure, which would activate the warning light correctly if it wasn't already, but doesn't diagnose a false warning at high pressure.
False Low Air Warning
When air pressure gauges indicate normal operating pressure but the low air pressure warning light remains on, it typically points to a fault in the warning system's electrical components, such as the pressure sensor or wiring.
- Gauges are primary indicator of pressure.
- Warning light is secondary indicator.
- Discrepancy suggests warning system fault.
Memory trick: Gauges say good, light says bad, sensor's wires are probably mad.