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Safety & Trades Practice Questions

CDL Air Brakes Practice Test Practice Questions

Commercial Driver's License Air Brakes Knowledge Test — Free cdl air brakes practice test questions covering low air pressure warnings, leakage rate, spring brakes, slack adjusters, and compressor governor checks. The real knowledge test is usually multiple choice, and the exact time limit and fee depend on your state DMV.

25
Total Questions
Varies by state
Time Limit
80%
Passing Score
Varies by DMV/state
Registration Fee

Free Sample Questions

Here are 5 free sample questions from our full bank of 550+ CDL Air Brakes Practice Testpractice questions. Try them out below — click "Show Answer" to reveal the correct response and explanation.

1

During the air brake system check, when must the low air pressure warning signal activate on most commercial vehicles?

ABefore air pressure drops below 60 psi
BOnly after the spring brakes have fully applied
CWhen air pressure reaches the governor cut-out level
DAny time the service brake pedal is pressed
2

With the engine off, wheels chocked, and air pressure built up, a single vehicle should not lose more than how much air pressure in one minute after the initial drop?

A1 psi
B2 psi
C3 psi
D5 psi
3

What happens if air pressure drops too low in a vehicle equipped with spring brakes?

AThe compressor automatically disconnects the parking brakes
BThe spring brakes may apply automatically
CThe service brakes become more powerful
DThe slack adjusters reset themselves
4

When checking manual slack adjusters during a pre-trip inspection, what amount of pushrod travel usually means the brake needs adjustment?

AAny movement at all
BMore than 1/2 inch
CExactly 1 inch
DMore than about 1 inch when pulled by hand
5

During the compressor governor check, what should happen when system pressure reaches the governor cut-out level?

AThe compressor should stop pumping air into the tanks
BThe low air warning should turn on
CThe spring brakes should apply immediately
DThe service brake pedal should lock in place

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About the CDL Air Brakes Practice Test

Format & Structure

Total Questions
25
Time Limit
Varies by state
Format
Multiple choice

Scoring & Cost

Passing Score
80%
Registration Fee
Varies by DMV/state

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Frequently Asked Questions

How many questions are on the CDL air brakes knowledge test?

The air brakes knowledge test is typically 25 multiple-choice questions, though the exact count can vary by state. Most states pull from the same CDL manual topics, so the core material is very similar: system parts, inspection steps, low air warnings, leakage checks, and safe braking.

What score do I need to pass the CDL air brakes test?

The usual passing score is 80%. For a 25-question test, that generally means answering at least 20 questions correctly. Your DMV can set the exact scoring and retake policy, so it is worth checking the state page before you schedule.

Is air brakes an endorsement on a CDL?

Air brakes are a little different from endorsements like HazMat or Tanker. If you do not pass the air brakes knowledge and skills requirements, your CDL will carry an air brake restriction, which means you cannot operate commercial vehicles equipped with air brakes. Many drivers still search for an air brakes endorsement practice test because the study process feels like preparing for an endorsement.

What should I study first for the CDL air brakes practice test?

Start with the inspection sequence: air compressor, governor cut-in and cut-out, leakage rate, low air warning, and spring brake application. Those checks show up again and again because they are both testable and important on the road. After that, review braking technique on downgrades and what to do when air pressure drops.

What is the low air pressure warning level for air brakes?

On most commercial vehicles, the low air warning must activate before air pressure drops below 60 psi. Some older vehicles or special systems may have slightly different details, but 60 psi is the number drivers are expected to know. If that warning comes on while driving, you should get stopped safely right away.

What are the air leakage limits for CDL air brakes?

After the initial pressure drop, a single vehicle should generally not lose more than 3 psi in one minute. A combination vehicle should not lose more than 4 psi in one minute. If the loss is higher, treat it as a serious defect because the system may not hold enough air for safe braking.

Do CDL air brake rules vary by state?

Yes, mainly in scheduling, fees, retake rules, and sometimes the time limit. The technical knowledge is based on federal CDL standards and the state CDL manual, so the big ideas stay consistent across the country. Always confirm the current fee and testing process with your own DMV before you go in.

How long should I study for the CDL air brakes test?

If you already understand basic truck systems, a few focused days may be enough. If air brakes are new to you, give yourself a week or two and practice the inspection steps out loud until they feel natural. The trick is not just memorizing numbers; you need to know what each check proves.

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