CDL Air Brakes TestInspecting Air Brake SystemsEasy
During a pre-trip inspection, a driver observes that the air pressure gauge shows 80 psi while the parking brake is set and the engine is off. The low air warning light is illuminated. What is the immediate correct action the driver should take?
- ARelease the parking brake and drive slowly to a service station.
- BFan off the air pressure further to test the spring brakes.
- CCheck for leaks in the air system immediately before driving.
- DStart the engine and build air pressure until the warning light turns off.
Show answer & explanationAnswer & explanation
Correct answer: D. Start the engine and build air pressure until the warning light turns off.
If the low air warning light is on, it indicates that the air pressure is below a safe operating level (typically 55-75 psi, but can be up to 85 psi on some vehicles). The immediate correct action is to start the engine and allow the air compressor to build pressure until the warning light goes out.
Why the other options are wrong
- A. Driving with low air pressure is extremely dangerous as service brakes may not function properly.
- B. Fanning off air pressure further would reduce it even more, which is unsafe when the warning is already active.
- C. While checking for leaks is important, the immediate priority is to build safe operating pressure. Leaks can be addressed once pressure is restored and stabilized.
Low Air Warning Action
When the low air warning light or buzzer activates, it signifies insufficient air pressure for safe braking. The immediate action is to build air pressure until the warning clears.
- Warning activates typically 55-75 psi.
- Indicates unsafe braking pressure.
- Start engine, build pressure immediately.
Memory trick: Low air warning, don't drive, build pressure high!