Wisconsin CDL Air Brakes Practice Test

The Wisconsin CDL Air Brakes test is a multiple-choice knowledge test you take for your commercial learner's permit. Wisconsin Department of Transportation, Division of Motor Vehicles (Wisconsin DMV) says you need 80% to pass (source).

Last updated Oct 7, 2026. FirstTry CDL is a CDL permit test prep site by Hive Asset Group, LLC.

By Scott Wilder, Editor

Last reviewed against the Wisconsin CDL manual on October 7, 2026

Scott Wilder on X | scottwilderhq.com

FirstTry CDL is a CDL permit test prep site by Hive Asset Group, LLC. It offers free exam-style practice tests built from the official CDL manual. FirstTry CDL is not affiliated with any DMV, FMCSA or government agency. Practice questions are exam-style questions built from the official CDL manual, not actual test questions.

Wisconsin CDL permit facts

What	What Wisconsin says	Source
Air Brakes pass mark	80%	Official page
Air Brakes test questions	25	Official page
CLP fee	$30, valid 180 days (Class A, B or C)	Official page
CLP holding period	Hold the CLP for 14 days before you take a skills test	Official page
Knowledge test retest rule	If you fail, you can retake no sooner than the next day. You may take the same test only five times in one year. After five tries you need special permission from DMV staff	Official page
Test languages	General knowledge, combination, air brakes, doubles and triples, passenger and tanker tests are offered in English, American Sign Language (video), Burmese, Croatian, Polish, Russian, Serbian and Spanish. The hazmat and school bus tests are English only. Translators and audio assist are not allowed on CDL tests.	Official page

20 question Air Brakes practice test

1. A vehicle without ABS brakes hard on a slick road and the non-steering wheels lock. What can happen?
1. A. The vehicle will always stop in a straight line
2. B. The brakes will cool down faster
3. C. The vehicle may skid, jackknife, or spin
4. D. Nothing, because only steering wheels matter
Show answer
Answer: C. The vehicle may skid, jackknife, or spin
Locked wheels other than the steering wheels can cause a skid, a jackknife, or a spin.
From the official CDL manual, section 5.4.2.
2. What is the electric heating device on an automatic air tank used for?
1. A. Warming air before it enters the brake chambers
2. B. Cooling the air compressor
3. C. Keeping the automatic drain from freezing
4. D. Boiling water out of the tank
Show answer
Answer: C. Keeping the automatic drain from freezing
The heater helps stop the automatic drain from freezing in cold weather.
From the official CDL manual, section 5.1.4.
3. In an s-cam brake, air pressure in the brake chamber pushes out the rod. What does the rod move next?
1. A. The wedge
2. B. The slack adjuster
3. C. The power screw
4. D. The brake drum
Show answer
Answer: B. The slack adjuster
The rod moves the slack adjuster, which twists the brake camshaft.
From the official CDL manual, section 5.1.8.
4. What does the emergency brake system use to stop the vehicle when a brake system fails?
1. A. A separate set of brakes used only in emergencies
2. B. Parts of the service and parking brake systems
3. C. Only the parking brake system
4. D. Only the trailer brakes
Show answer
Answer: B. Parts of the service and parking brake systems
The emergency system shares parts of the service and parking brake systems.
From the official CDL manual, section 5.
5. You have a modulating control valve. What happens when you move the lever farther?
1. A. The spring brakes come on more softly
2. B. The spring brakes release
3. C. The spring brakes come on harder
4. D. The air tanks drain
Show answer
Answer: C. The spring brakes come on harder
The more you move the control lever, the harder the spring brakes come on.
From the official CDL manual, section 5.1.15.
6. Your air compressor has its own oil supply. What should you do before driving?
1. A. Drain the compressor oil
2. B. Add alcohol to the oil
3. C. Check the compressor oil level
4. D. Nothing, because engine oil is all that matters
Show answer
Answer: C. Check the compressor oil level
A compressor with its own oil supply needs its oil level checked before you drive.
From the official CDL manual, section 5.1.1.
7. Where is the safety relief valve installed?
1. A. In the first tank the compressor pumps air to
2. B. In the last tank at the end of the system
3. C. Next to the brake pedal in the cab
4. D. In each of the brake chambers at the wheels
Show answer
Answer: A. In the first tank the compressor pumps air to
The valve sits in the first tank the compressor fills.
From the official CDL manual, section 5.1.6.
8. What do the brake shoes pushing on the drum create besides slowing the vehicle?
1. A. Air pressure
2. B. Heat
3. C. Extra air in the tanks
4. D. Cold air
Show answer
Answer: B. Heat
Friction between the shoes and drum slows the vehicle and creates heat.
From the official CDL manual, section 5.1.8.
9. Your ABS stops working while you drive. What do you have, and what should you do?
1. A. Regular brakes; drive normally and get the system serviced soon
2. B. No brakes at all; stop at once and call for a tow
3. C. Only rear brakes; drive very slowly
4. D. Weaker brakes; pump the pedal on every stop
Show answer
Answer: A. Regular brakes; drive normally and get the system serviced soon
The regular brakes still work, so you drive normally and have the ABS serviced soon.
From the official CDL manual, section 5.4.2.
10. On a downgrade, when do you apply the brakes again after releasing them?
1. A. After you reach the bottom
2. B. Right after you release them
3. C. When your speed rises back to your safe speed
4. D. When the brake lights go off
Show answer
Answer: C. When your speed rises back to your safe speed
The manual says to repeat when speed has increased to your safe speed.
From the official CDL manual, section 5.4.6.
11. How do you open a manually operated air tank drain valve?
1. A. Press the brake pedal until the air stops
2. B. Push in the yellow parking brake knob
3. C. Turn it a quarter turn or pull its cable
4. D. Turn it several full turns with a wrench
Show answer
Answer: C. Turn it a quarter turn or pull its cable
Manual drain valves work by a quarter turn or by pulling a cable.
From the official CDL manual, section 5.1.4.
12. Only your trailer has ABS. You lose steering control and the tractor starts to jackknife. What should you do?
1. A. Brake harder to straighten the trailer
2. B. Turn the wheel sharply and keep braking
3. C. Let up on the brakes if it is safe, until you gain control
4. D. Shift to a higher gear
Show answer
Answer: C. Let up on the brakes if it is safe, until you gain control
Let up on the brakes, if you can do so safely, until you gain control.
From the official CDL manual, section 5.4.2.
13. Which pair shows the typical pressures where the compressor starts and stops pumping?
1. A. Starts at about 100 psi, stops at about 125 psi
2. B. Starts at about 85 psi, stops at about 100 psi
3. C. Starts at about 125 psi, stops at about 100 psi
4. D. Starts at about 20 psi, stops at about 45 psi
Show answer
Answer: A. Starts at about 100 psi, stops at about 125 psi
The manual says pumping should start at about 100 psi and stop at about 125 psi (check manufacturer's specifications).
From the official CDL manual, section 5.3.3.
14. When should you use the parking brakes?
1. A. Only on hills
2. B. Whenever you park
3. C. Only in cold weather
4. D. Only when the tanks are low
Show answer
Answer: B. Whenever you park
The manual says to use the parking brakes whenever you park.
From the official CDL manual, section 5.1.15.
15. How may an air compressor be cooled?
1. A. By air or by the engine cooling system
2. B. By the brake fluid only
3. C. By the air tanks only
4. D. By the governor
Show answer
Answer: A. By air or by the engine cooling system
The compressor may be air cooled or cooled by the engine cooling system.
From the official CDL manual, section 5.1.1.
16. You are making a normal stop in a truck with a manual transmission. When should you push the clutch in?
1. A. When engine rpm has dropped close to idle
2. B. As soon as you take your foot off the accelerator
3. C. Before you start to brake
4. D. When the brake pedal is halfway down
Show answer
Answer: A. When engine rpm has dropped close to idle
The manual says to wait to push the clutch in until engine rpm is down close to idle.
From the official CDL manual, section 5.4.1.
17. A visible low air pressure warning must come on before tank pressure falls below what?
1. A. 20 psi
2. B. 55 psi
3. C. 80 psi
4. D. 100 psi
Show answer
Answer: B. 55 psi
The warning signal must come on before pressure falls below 55 psi.
From the official CDL manual, section 5.1.11.
18. In a dual air brake system, which brakes does one system typically operate?
1. A. Only the trailer brakes
2. B. Only the parking brakes
3. C. The regular brakes on the rear axle or axles
4. D. Only the engine brake
Show answer
Answer: C. The regular brakes on the rear axle or axles
One system typically operates the regular brakes on the rear axle or axles.
From the official CDL manual, section 5.2.
19. What do you look for on the air hoses connected to the brake chambers?
1. A. Paint chips
2. B. Bright colors
3. C. Extra length
4. D. Cuts or wear from rubbing
Show answer
Answer: D. Cuts or wear from rubbing
The manual says to make sure the hoses are not cut or worn from rubbing.
From the official CDL manual, section 5.3.2.
20. You will be away from your vehicle for only a short time. What should you do?
1. A. Apply the parking brakes or chock the wheels
2. B. Nothing, because it is only a short time
3. C. Leave it in gear with the engine running and no brakes
4. D. Turn the front wheels and leave the brakes off
Show answer
Answer: A. Apply the parking brakes or chock the wheels
Never leave a vehicle unattended without applying the parking brakes or chocking the wheels, even for a short time.
From the official CDL manual, section 5.4.8.

Wisconsin CDL Air Brakes questions

What score do you need to pass the Wisconsin CDL Air Brakes test?

Wisconsin says you need 80% to pass the Air Brakes test.

Is the Wisconsin CDL Air Brakes test the same as other states?

The Air Brakes test is built on the same federal knowledge standards in every state, so the topics match the CDL manual. Wisconsin uses its own handbook: https://wisconsindot.gov/Documents/dmv/shared/bds356-cdl-manual.pdf

How much does a CDL permit cost in Wisconsin?

CLP fee: $30, valid 180 days (Class A, B or C).

What languages is the Wisconsin CDL knowledge test offered in?

General knowledge, combination, air brakes, doubles and triples, passenger and tanker tests are offered in English, American Sign Language (video), Burmese, Croatian, Polish, Russian, Serbian and Spanish. The hazmat and school bus tests are English only. Translators and audio assist are not allowed on CDL tests.

Sources

https://wisconsindot.gov/Pages/dmv/com-drv-vehs/rqts-for-cdl/cdl-requirements.aspx
https://wisconsindot.gov/Pages/dmv/vehicles/title-plates/dmv-fees.aspx
https://wisconsindot.gov/Pages/dmv/teen-driver/teen-hw-aply/knowledge.aspx
https://wisconsindot.gov/Documents/dmv/shared/bds356-cdl-manual.pdf
Manual sections used in this test: 5; 5.1.1; 5.1.11; 5.1.15; 5.1.4; 5.1.6; 5.1.8; 5.2; 5.3.2; 5.3.3; 5.4.1; 5.4.2; 5.4.6; 5.4.8

Air Brakes practice test in nearby states