Home › CDL Practice Tests › Air Brakes Questions › Question 144
During a pre-trip air brake check with the engine off and the brakes applied, you hear air hissing steadily from one brake chamber. What does this most likely mean, and what must you do?
- A.It is the normal sound of the quick-release valve and can be ignored
- B.The treadle valve is recharging the chamber and the sound will stop on its own
- C.A leaking chamber diaphragm or line is losing air under pressure; the vehicle must not be driven until it is repaired
- D.The ABS modulator is cycling and the truck is ready to roll
Correct answer
C. A leaking chamber diaphragm or line is losing air under pressure; the vehicle must not be driven until it is repaired
Why
Air should hold steady once the brakes are applied, so continuous hissing at a chamber points to a torn diaphragm or failed line that will drain the system under working pressure. A chamber leaking like this is an out-of-service defect, not a note-it-and-go item.
Manual topic: Air Brakes - Brake Inspection · From the Air Brakes practice bank (AB-144).