CDL Air Brakes TestInspecting Air Brake SystemsMedium
During a pre-trip inspection, a driver performs the low air pressure warning test. The low air pressure warning device should activate when the air pressure in the tanks drops to no less than what PSI?
- A80 psi
- B50 psi
- C70 psi
- D60 psi
Show answer & explanationAnswer & explanation
Correct answer: D. 60 psi
The low air pressure warning device (light and/or buzzer) is designed to activate when the air pressure in the service air tanks falls below 60 psi (or half of the governor cut-out pressure on older vehicles). This warns the driver that air pressure is critically low.
Why the other options are wrong
- A. 80 psi is too high; the warning should activate at a lower, more critical pressure.
- B. 50 psi is too low; the warning must come on before pressure drops this far.
- C. 70 psi is also too high for the critical warning.
Low Air Pressure Warning
A safety feature in air brake systems that alerts the driver when air pressure drops to a dangerously low level, typically below 60 psi.
- Activates a visual (light) and/or audible (buzzer) warning.
- Critical for driver awareness of potential brake failure.
- Must be tested during pre-trip inspection.
Memory trick: Sixty's the scary PSI, or your brakes might say goodbye!