A technician is troubleshooting a dual air brake system where the low air pressure warning for the primary system activates correctly, but the warning for the secondary system never activates, even when its pressure drops below 60 psi. What is the most probable cause?
- AA defective pressure sensor or wiring for the secondary system's low air warning.
- BA faulty air compressor.
- CThe secondary system's air tank drain valve is open.
- DA leak in the primary air line.
Show answer & explanationAnswer & explanation
Correct answer: A. A defective pressure sensor or wiring for the secondary system's low air warning.
If the secondary system's pressure drops below the warning threshold (60 psi) but the warning does not activate, it points to a failure in the warning mechanism itself for that specific system. This is most commonly a faulty pressure sensor, a wiring issue, or a defective warning light/buzzer for the secondary system. A faulty compressor would affect both systems. A leak in the primary line wouldn't explain the secondary warning failure. An open drain valve would cause pressure loss but wouldn't prevent the warning from activating if the sensor was working.
Why the other options are wrong
- B. A faulty air compressor would affect air pressure buildup in both systems.
- C. An open drain valve would cause pressure loss, but the warning should still activate if the sensor works.
- D. A leak in the primary line would cause the primary warning, not prevent the secondary warning.
Low Air Warning Failure
When a low air pressure warning device (light/buzzer) fails to activate despite the air pressure in its associated system dropping below the required threshold (60 psi).
- Indicates a fault in the sensor, wiring, or alarm unit.
- Compromises driver awareness of critical air loss.
- Must be repaired immediately for safety.
Memory trick: If the gauge drops but the alarm stays quiet, check the sensor.