CDL Air Brakes TestDual Air Brake SystemsMedium
A driver notices the low air pressure warning light and buzzer activate while operating a vehicle equipped with a dual air brake system. The gauges indicate that both the primary and secondary systems are above 80 psi. What is the most likely cause of this warning?
- AA faulty air compressor that is not building pressure correctly.
- BA leak in the air lines leading to the warning system itself.
- CA malfunction in the low air pressure warning switch or sensor.
- DThe vehicle's parking brake is partially engaged, triggering a false alarm.
Show answer & explanationAnswer & explanation
Correct answer: C. A malfunction in the low air pressure warning switch or sensor.
If the air pressure gauges show adequate pressure (above 60 psi, typically 80 psi or more), but the low air warning is active, it strongly suggests a fault with the warning system's components rather than an actual low air condition.
Why the other options are wrong
- A. If the compressor was faulty, the gauges would show low pressure, contradicting the scenario.
- B. A leak in the warning system's lines is less common and usually wouldn't trigger the warning unless it caused a pressure drop elsewhere, which the gauges would reflect.
- D. While a parking brake can have air-related warnings, it typically indicates the brake is applied or releasing, not a general low air pressure warning when gauges are normal.
Low Air Pressure Warning System Troubleshooting
The low air pressure warning system (light and buzzer) activates when air pressure drops below 60 psi in either the primary or secondary system.
- Activates at 60 psi or less.
- Must work before air pressure builds to 60 psi.
- If gauges are normal but warning is active, suspect the sensor/switch.
Memory trick: Gauges say good, light says bad, sensor's mad.