CDL Air Brakes TestAir Brake System PartsMedium
A driver performs a brake test and notes that the red low air pressure warning light and buzzer come on at 70 psi and turn off at 80 psi. What does this indicate about the low air pressure warning system?
- AThe warning system is functioning correctly, as it activates above the minimum requirement.
- BThe warning system is malfunctioning, as it should activate at a lower pressure.
- CThe air compressor governor is set too high.
- DThe warning system is activating too late, indicating a sensor fault.
Show answer & explanationAnswer & explanation
Correct answer: A. The warning system is functioning correctly, as it activates above the minimum requirement.
Federal regulations require the low air pressure warning system to activate when air pressure drops to or below 60 psi (or half of the governor cut-out pressure on older vehicles). Activating at 70 psi is above this minimum requirement, meaning the system is functioning correctly and providing an early warning.
Why the other options are wrong
- B. The warning system is designed to activate at or above 60 psi, so 70 psi activation is within acceptable limits, not a malfunction.
- C. The air compressor governor controls the cut-in/cut-out pressure for the compressor, not the activation threshold of the low air warning system.
- D. Activating at 70 psi is earlier than the critical 60 psi threshold, so it's activating appropriately, not too late.
Low Air Pressure Warning Threshold
The specific air pressure level (typically 60 psi or half of governor cut-out) at which the low air pressure warning light and buzzer must activate.
- Mandated by federal regulations for air brake systems.
- Provides critical warning to the driver before spring brakes engage.
- Ensures driver awareness of system air pressure loss.
Memory trick: Warning At Sixty, Safe and Swiftly.