CDL General Knowledge TestDriving SafelyMedium
A commercial driver is operating a vehicle equipped with air brakes. The driver notices that the air pressure warning light comes on and the buzzer sounds. What is the minimum air pressure at which this warning system must activate?
- A60 psi
- B80 psi
- C40 psi
- D20 psi
Show answer & explanationAnswer & explanation
Correct answer: A. 60 psi
Federal regulations require that the low air pressure warning system (light and buzzer) in an air brake vehicle must activate when the air pressure drops below 60 psi in the air tanks, or below half the compressor governor cut-out pressure on older vehicles.
Why the other options are wrong
- B. 80 psi is typically a safe operating pressure, not the warning threshold.
- C. 40 psi is dangerously low and could indicate a significant problem if the warning wasn't already active.
- D. 20 psi is extremely low, indicating an imminent loss of braking capability, far below the required warning threshold.
Low Air Pressure Warning
A safety system in air brake vehicles that alerts the driver when air tank pressure falls below a critical level, indicating a potential braking system failure.
- Activates with light and buzzer
- Warns of insufficient air for braking
- Mandated by federal regulations
Memory trick: Sixty psi means Serious problem.