CDL Air Brakes Practice Test 2026: Sample Questions and Answers
By Rish P · September 10, 2026 · Updated November 3, 2026
The CDL air brakes test is a separate knowledge test that removes the air-brake restriction from your license, and you need it if you will drive a commercial vehicle equipped with air brakes. It is usually about 25 questions with an 80% passing score, taken alongside your general knowledge test when you get your commercial learner's permit (CLP). If you need ELDT, RoadCert offers FMCSA-registered online ELDT theory for Class A, Class B, Hazmat and Passenger, and we report your completion to the FMCSA for you.
What the air brakes test covers
The questions come from the air brakes section of your state's CDL manual: how air brake systems work, the difference between service, parking, and emergency brakes, the low-air-pressure warning, the supply pressure gauge, slack adjusters, and the proper way to test air brakes during a pre-trip inspection. Dual air brake systems and how to respond to air loss are common topics.
Why it matters
If you do not pass air brakes, your CDL gets an "L" restriction that legally bars you from driving any commercial vehicle with air brakes, which is most trucks. Passing it keeps every job open to you.
Sample questions
- If your truck has a dual air brake system and one system loses pressure, you should:
- a) Keep driving normally
- b) Bring the vehicle to a safe stop and continue only after repairs
- c) Pump the brakes
- d) Turn off the engine
- The air compressor governor controls:
- a) Engine speed
- b) When the compressor pumps air into the tanks
- c) The parking brake
- d) Trailer connections
- The low-air-pressure warning must come on before pressure drops below:
- a) 20 psi
- b) 40 psi
- c) 60 psi
- d) 100 psi
- To test that the air brake system holds pressure, you should:
- a) Rev the engine
- b) With a fully charged system, turn off the engine, release the parking brake, and time the air-pressure drop
- c) Drive at highway speed
- d) Pump the brakes 10 times
Answers: 1) b. 2) b. 3) c, before 60 psi. 4) b.
How to pass
Read the air brakes chapter of your CDL manual, then drill practice tests until you are steadily above 80%. Once you pass air brakes and general knowledge, your next step is completing your ELDT (Entry-Level Driver Training) theory before your skills test.
Sources
Checked November 2, 2026.
- eCFR: 49 CFR 383.95, Restrictions (air brake): Failing the air brake knowledge test puts a restriction on the CLP or CDL barring any vehicle with air brakes.
- eCFR: 49 CFR 383.135, Passing knowledge and skills tests: Applicants must answer at least 80 percent correctly to pass each knowledge test, including air brakes.
- eCFR: 49 CFR 383.25, Commercial learner's permit (CLP): The air brakes and general knowledge tests are taken when you apply for a commercial learner's permit.
- FMCSA: Entry-Level Driver Training (ELDT): ELDT theory must be completed before the skills test.
Frequently asked questions
Do I need to pass the air brakes test to get a CDL?
Yes, you need to pass the air brakes knowledge test if you will drive any commercial vehicle equipped with air brakes, which includes most trucks and buses. If you skip it or fail it, your CLP or CDL carries an air-brake restriction (L) that bars you from driving those vehicles until you pass.
How many questions are on the CDL air brakes test and what score do I need?
The air brakes test usually has about 25 multiple-choice questions, and you need at least 80% correct to pass. Federal rules set the 80% minimum for each knowledge test, but the exact number of questions varies slightly by state, so check your state's CDL manual or licensing agency for the current count.
What happens if I fail the CDL air brakes test?
If you fail the air brakes test, you can still be issued a CLP or CDL, but it will carry an L restriction that bars you from driving any commercial vehicle with air brakes. You can retake the test later to remove the restriction, and your state sets the retest rules and any waiting period.
Is the air brakes test part of the general knowledge test?
No, the air brakes test is a separate knowledge test that you take in addition to the general knowledge test when you get your commercial learner's permit (CLP). Passing the general knowledge test alone does not remove the air-brake restriction, so you need to pass both if you plan to drive air-brake vehicles.
What is the best way to study for the CDL air brakes test?
The best way to study is to read the air brakes section of your state's CDL manual, then take practice tests until you score steadily above 80%. Focus on dual air systems, the low-air-pressure warning, the compressor governor, and how to test the brakes during a pre-trip inspection, since those topics come up often.
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