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Air Brakes Practice Question 8

Restriction L if not passedAir Brakes · Question 8

When inspecting the air brake system, you should first build pressure to:

• AAbove the warning threshold and then test the warning signal
• BMaximum cut-out and then immediately drive
• C50 psi and continue
• D150 psi and start engine

Correct answer: A. Above the warning threshold and then test the warning signal

Why: Build to governor cut-out, then turn off the engine and fan the brakes to drop pressure. The warning signal must come on before pressure falls below 60 psi.

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

• Q13. The trailer hand valve (trolley valve, Johnson bar) should be used:
• Q26. If the ABS warning light stays on after start-up:
• Q39. A driver who hears continuous air leakage during a leak-down test should:
• Q52. Air dryers in the system serve to:
• Q3. Typical compressor cut-out pressure is approximately:

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.