Home › CDL Practice Tests › Air Brakes Questions › Question 90
During the pop-out test, after fanning the brakes down, what pressures tell the full story of a healthy system?
- A.Warning at 120 psi and knobs at 100 psi
- B.Warning only at 0 psi with no knob movement
- C.Warning on before 60 psi, then tractor/trailer protection and spring knobs popping in roughly the 20 to 45 psi range
- D.No warning at any pressure is acceptable
Correct answer
C. Warning on before 60 psi, then tractor/trailer protection and spring knobs popping in roughly the 20 to 45 psi range
Why
The descending sequence validates three separate protections in one test. Any step arriving late, early, or not at all identifies which device needs repair before the trip.
Manual topic: Air Brakes - Air Leakage and Brake Tests · From the Air Brakes practice bank (AB-090).