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Air Brakes Practice Question 6

Restriction L if not passedAir Brakes · Question 6

The air brake system air loss rate (with engine off, brakes released) for a single vehicle should not exceed:

• A1 psi per minute
• B2 psi per minute
• C3 psi per minute
• D5 psi per minute

Correct answer: B. 2 psi per minute

Why: Single vehicle: maximum air loss is 2 psi per minute with brakes released. With brakes applied, 3 psi per minute. Combination vehicles allow slightly higher rates.

How this question fits the Air Brakes test

An air brake failure on a loaded combination vehicle can cause runaway, jackknife, or fire. The CDL Air Brakes test exists because air systems behave very differently from hydraulic brakes — drivers must understand pressure build, air loss tolerance, and stopping distance under load.

Study technique for this topic

Memorize the seven steps of the air brake pre-trip check, the leak-down rates for single and combination vehicles, the warning signal pressure threshold, and the spring brake automatic application pressure range. Practice the order of operations — never rely on muscle memory in the booth.

Related Air Brakes practice questions

• Q12. The service line (control line) is connected by the:
• Q25. Anti-lock braking systems (ABS) on tractors and trailers are intended to:
• Q38. Air brake supply pressure should generally fall between:
• Q51. When testing the spring brakes during pre-trip you should expect:
• Q2. The compressor governor controls:

Continue your CDL preparation

The Air Brakes portion of the CDL knowledge exam covers more than this single question. Use this site's full Air Brakes bank to drill every topic, then test yourself with one of our state-specific practice sets to confirm you are ready for the actual DMV exam in your state. Always check your state's CDL handbook for any local addenda before the test day.

If you are still building your overall CDL foundation, start with the General Knowledge bank — every CDL applicant must pass it — and then work outward to the endorsements you plan to add.