During a pre-trip air brake check, with the system fully charged, the engine off, and the parking brake released, what is the maximum acceptable air pressure loss rate?

Explanation

With the air system fully charged, the engine off, and the parking brake released, the air pressure loss rate must be less than 2 psi per minute for a single vehicle or less than 3 psi per minute for a combination vehicle to pass the check. 49 CFR 383.111(b)(5) requires CDL applicants to know the procedures for conducting safe and accurate pre-trip inspections, the required-knowledge area this leakage test falls under; the specific 2 and 3 psi figures are standard driver-training content from the manual, not numbers stated in the CFR paragraph itself. A flat 10 psi per minute standard is wrong because it is far looser than the actual figures and does not distinguish single from combination vehicles. Requiring zero measurable loss is wrong because a small amount of leakage is expected and tolerated up to the stated rate; the test has a defined limit, not a zero-tolerance standard. Testing only with the engine running is backwards; this specific test is run with the engine off precisely to isolate leakage in the stored air supply.

Source: 49 CFR 383.111(b)(5)