Driving · Commercial
CDL Air Brakes Test
The knowledge test you pass to drive a truck or bus with air brakes without the air brake restriction: parts, dual systems, inspection checks and braking technique.
Questions last checked against the official sources on October 10, 2026.
The real exam at a glance
- Questions
- 25 (varies by state)
- To pass
- 80% (20 of 25)
- Time
- About 25 minutes (varies by state)
- Fail it
- Air brake restriction on your CDL
- Based on
- Section 5 of your state's CDL manual
What you'll practise
Try a question
Before driving a vehicle with a dual air system, what minimum pressure should build up in both systems?
- 55 psi
- 100 psi
- 85 psi
- 125 psi
Show the answer
B. 100 psi — Allow time for the compressor to build up a minimum of 100 psi in both the primary and secondary systems (CDL Manual 5.2)
Sample questions by topic (in English)
Ask the examiner
Ask about this exam: why an answer is wrong, a grammar point, or “quiz me on …”.
Practice help only — no immigration, citizenship, legal or eligibility advice. For your application, ask the official authority. Answers can be wrong; check important facts. Chats aren't saved on our servers.
Questions about the CDL Air Brakes
Is this the official CDL Air Brakes?
No. Semplr is independent and not affiliated with the exam body. We write every question ourselves, in the official format and at the official level.
What is the real CDL Air Brakes like?
Questions: 25 (varies by state). To pass: 80% (20 of 25). Time: About 25 minutes (varies by state). Fail it: Air brake restriction on your CDL. Based on: Section 5 of your state's CDL manual.
How is my practice marked?
Instantly. You see your score against the pass mark, and an explanation for every question — including the ones you got right.
Can I take it on my phone?
Yes. The whole mock exam works on a phone, and your progress is saved in your browser.
Ready for a full run?
One sitting, real timing, then your score against the pass mark.
Start the free mock exam