CDL Air Brakes Practice Test
If your commercial vehicle uses air brakes, your state requires you to pass the CDL Air Brakes knowledge test to remove the L restriction from your license. Skip it and you're limited to non-air-brake vehicles — which rules out most tractor-trailers, straight trucks over 26,000 lb GVWR, and virtually every long-haul job.
Our free Air Brakes practice test covers everything the DMV can test you on: how the air brake system works, the parts that make up the system, how to inspect it on a pre-trip, how to test it, and how it behaves in an emergency. Every question is drawn from public FMCSA regulations and the CDL manual your state DMV publishes.
What this test covers
- Parts of the air brake system: compressor, governor, reservoirs, foot valve, brake chambers, slack adjusters, S-cam brakes
- Dual air brake systems and split braking
- Spring brakes and parking brakes
- Antilock braking systems (ABS)
- Air brake pre-trip inspection (leak-down, governor cut-in/cut-out, low-air warning, spring brake activation)
- Stopping distance and brake fade
- Emergency braking and brake failure procedures
How to study
- Memorize the seven-step air brake test in order — several DMV questions ask you to identify what you check and why.
- Learn the pressure targets by heart: low-air warning at 60 psi or below, spring brakes at 20–45 psi.
- Practice the pre-trip air brake wording out loud. Many CDL road exams require you to say it back to the examiner.
Frequently asked questions
- How many questions are on the Air Brakes endorsement test?
- Most states give a 25-question Air Brakes test that requires 80% (20 out of 25) to pass.
- Do I need the Air Brakes test if I drive a truck with hydraulic brakes?
- No. The Air Brakes endorsement is only required if your commercial vehicle is equipped with air brakes. If you take your CDL road test in a hydraulic-braked vehicle, an L restriction is added to your license.
Ready to start?
Practice this CDL topic free — no account needed for your first session. Unlock the full course when you're ready.