Maximum allowable trailer-brake leakage rate (engine off, brakes released, combination vehicle) is:
Correct. Combination vehicles: no more than 3 psi/min with brakes released, 4 psi/min with brakes applied.
CDL Practice Question #208
Category: Combination Vehicles
Why this question matters
This question is one of 55 in our Combination Vehicles bank. The reasoning above comes directly from the AAMVA CDL Manual, the source document used by every U.S. state DMV. Memorizing the underlying rule — not just the letter answer — is what separates passing on the first attempt from a return trip and another fee.