Alabama CDL General Practice Test 2026 – Complete Prep Resource

This test checks air brake integrity by measuring how quickly the system loses air when the engine is off and the brakes are applied. With the engine off, the compressor isn’t pumping, so any loss in pressure comes from leaks in hoses, fittings, or chambers. The brakes being applied puts the system under load, so monitoring the drop over one minute shows whether the leaks are within safe limits. For a straight truck or bus, the allowed drop is three psi in one minute. If the pressure falls by more than three psi, it indicates excessive leakage that could compromise braking performance, and the vehicle would fail the test. So, the correct limit to expect is a maximum of three psi per minute when brakes are applied and the engine is off.