Home › CDL Practice Tests › General Knowledge Questions › Question 6
At what point must the low air pressure warning device on an air brake system activate?
- A.Only after the engine is shut off
- B.Before pressure falls below 60 psi
- C.At 90 psi, when the compressor cuts out
- D.At 20 psi, when the spring brakes pop out
Correct answer
B. Before pressure falls below 60 psi
Why
The warning light and buzzer must come on before tank pressure drops below 60 psi, giving the driver time to stop safely. By 20 to 45 psi the spring brakes may apply on their own, which is far too late for a first warning.
Manual topic: Vehicle Inspection - Brake System · From the General Knowledge practice bank (GK-006).