Home › CDL Practice Tests › Combination Vehicles Questions › Question 15
What can happen if the service and supply air lines are crossed when connected?
- A.Nothing, the lines are interchangeable
- B.Only the trailer lights will fail
- C.The engine will lose power
- D.The trailer brakes may not work correctly, and the trailer spring brakes may not release or may apply unexpectedly
Correct answer
D. The trailer brakes may not work correctly, and the trailer spring brakes may not release or may apply unexpectedly
Why
The supply line charges the trailer and controls its spring brakes, while the service line signals braking. Crossing them reverses those jobs and can leave you with dragging or unresponsive trailer brakes.
Manual topic: Combination Vehicles - Coupling · From the Combination Vehicles practice bank (CV-015).