North Carolina CDL Air Brakes Practice Test

The North Carolina CDL Air Brakes test is a multiple-choice knowledge test you take for your commercial learner's permit. North Carolina Division of Motor Vehicles (NCDMV), part of NCDOT says you need 80% to pass (source).

Last updated Oct 15, 2026. FirstTry CDL is a CDL permit test prep site by Hive Asset Group, LLC.

By Scott Wilder, Editor

Last reviewed against the North Carolina CDL manual on October 15, 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.

North Carolina CDL permit facts

What	What North Carolina says	Source
Air Brakes pass mark	80%	Official page
CLP fee	$25.50 (listed as Learner's Permit in the manual fee list)	Official page
CLP validity	180 days. It can be renewed once, also for 180 days.	Official page
Test languages	The CDL pages do not name the languages for CDL tests and give no English-only rule. For regular license tests NCDMV says tests are offered in different languages and oral tests are available on request, and you can ask for an ASL or language interpreter online.	Official page

20 question Air Brakes practice test

1. 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.
2. On a long, steep downgrade, what is the role of the brakes?
1. A. They are the main way to hold your speed
2. B. They are used only for the final stop at the bottom
3. C. They only supplement the braking effect of the engine
4. D. They replace engine braking once you reach a low gear
Show answer
Answer: C. They only supplement the braking effect of the engine
The manual says brakes are only a supplement to engine braking on a long or steep downgrade.
From the official CDL manual, section 5.4.6.
3. What does the parking brake control look like on newer air brake vehicles?
1. A. A red, octagon-shaped push-pull knob
2. B. A blue, round turn knob
3. C. A yellow, square foot pedal
4. D. A yellow, diamond-shaped push-pull knob
Show answer
Answer: D. A yellow, diamond-shaped push-pull knob
The parking brake control is a diamond-shaped, yellow, push-pull knob.
From the official CDL manual, section 5.1.15.
4. Tractor and straight truck spring brakes come fully on when air pressure drops to what range?
1. A. 5 to 15 psi
2. B. 55 to 80 psi
3. C. 20 to 45 psi
4. D. 100 to 125 psi
Show answer
Answer: C. 20 to 45 psi
The manual gives a range of 20 to 45 psi, typically 20 to 30 psi.
From the official CDL manual, section 5.1.14.
5. The low air warning light and buzzer just came on while you drive. What should you do?
1. A. Bring the vehicle to a safe stop right away
2. B. Keep driving until the spring brakes come on
3. C. Pump the brake pedal to build pressure
4. D. Drive slowly to the next exit
Show answer
Answer: A. Bring the vehicle to a safe stop right away
You should stop right away while you still control the brakes, and not wait for the spring brakes.
From the official CDL manual, section 5.1.14.
6. A leak lets all the air out of the brake system. What happens to the spring brakes?
1. A. They stay released until you pull the parking brake knob
2. B. The springs put on the brakes
3. C. Only the front spring brakes apply
4. D. They stay released until the tanks are refilled
Show answer
Answer: B. The springs put on the brakes
When all the air is lost, the springs apply the brakes.
From the official CDL manual, section 5.1.14.
7. What does the air compressor do in an air brake system?
1. A. Sends air to the brake chambers when you press the pedal
2. B. Controls when the spring brakes apply
3. C. Pumps air into the air storage tanks
4. D. Warns you when air pressure drops
Show answer
Answer: C. Pumps air into the air storage tanks
The compressor's job is to pump air into the storage tanks.
From the official CDL manual, section 5.1.1.
8. Where do water and oil collect in an air tank?
1. A. In the top of the tank
2. B. Along the sides of the tank
3. C. In the air lines only
4. D. In the bottom of the tank
Show answer
Answer: D. In the bottom of the tank
The water and oil tend to collect in the bottom of the air tank, where the drain valve is.
From the official CDL manual, section 5.1.4.
9. In controlled braking, you released the brakes to make a larger steering change. When do you re-apply them?
1. A. After you stop steering for ten seconds
2. B. As soon as you can
3. C. Only after the vehicle stops
4. D. Never, coast to a stop
Show answer
Answer: B. As soon as you can
Re-apply the brakes as soon as you can.
From the official CDL manual, section 5.4.3.
10. On large buses, low pressure warning devices commonly signal at about what pressure?
1. A. 55 psi
2. B. 20 to 30 psi
3. C. 125 psi
4. D. 80 to 85 psi
Show answer
Answer: D. 80 to 85 psi
Large buses often have warnings that signal at 80 to 85 psi.
From the official CDL manual, section 5.1.11.
11. You pull hard on a slack adjuster. Movement of more than what distance at the push rod means it probably needs adjusting?
1. A. About one quarter inch
2. B. About one inch
3. C. About three inches
4. D. About six inches
Show answer
Answer: B. About one inch
A slack adjuster that moves more than about one inch where the push rod attaches probably needs adjustment.
From the official CDL manual, section 5.3.2.
12. What is a dual air brake system?
1. A. One air system that uses two air compressors
2. B. Two complete sets of brake pedals and controls
3. C. Two separate systems with a single set of controls
4. D. A system with extra tanks for the trailer only
Show answer
Answer: C. Two separate systems with a single set of controls
A dual system has two separate air systems that are worked by a single set of controls.
From the official CDL manual, section 5.2.
13. Why is the s-cam called an s-cam?
1. A. It stands for steel cam
2. B. It stands for safety cam
3. C. It was named after its inventor
4. D. It is shaped like the letter S
Show answer
Answer: D. It is shaped like the letter S
The s-cam is named because it is shaped like the letter S.
From the official CDL manual, section 5.1.8.
14. Why should you do the service brake test before you drive on the road?
1. A. It warms up the brake drums
2. B. It sets the slack adjusters
3. C. It builds air pressure faster
4. D. It may show problems you would not know about until you needed the brakes
Show answer
Answer: D. It may show problems you would not know about until you needed the brakes
The test may show brake problems you would not find until you needed the brakes on the road.
From the official CDL manual, section 5.3.3.
15. It starts to rain. Where should you set the front brake limiting valve control?
1. A. Normal
2. B. Slippery
3. C. Halfway between the two settings
4. D. Slippery, but only if there is ice
Show answer
Answer: A. Normal
The control should stay in normal for normal stopping power.
From the official CDL manual, section 5.1.13.
16. What happens when you push the brake pedal down harder?
1. A. Less air pressure is applied
2. B. More air pressure is applied
3. C. The compressor stops
4. D. The governor opens the safety valve
Show answer
Answer: B. More air pressure is applied
Pushing the pedal down harder applies more air pressure.
From the official CDL manual, section 5.1.7.
17. A truck was built in 1996. What kind of slack adjusters does it have?
1. A. Manual slack adjusters only
2. B. No slack adjusters
3. C. Automatic slack adjusters
4. D. Slack adjusters on the front axle only
Show answer
Answer: C. Automatic slack adjusters
The manual says all vehicles built since 1994 have automatic slack adjusters.
From the official CDL manual, section 5.3.2.
18. Why should you never push the brake pedal down when the spring brakes are on?
1. A. The springs and air together could damage the brakes
2. B. It lets compressed air out of the tanks
3. C. It releases the spring brakes at once
4. D. It turns off the low air pressure warning
Show answer
Answer: A. The springs and air together could damage the brakes
Springs and air pressure pushing together could damage the brakes.
From the official CDL manual, section 5.1.15.
19. At 55 mph on dry pavement, brake lag adds about how many feet to your stopping distance?
1. A. About 8 feet
2. B. About 100 feet
3. C. About 32 feet
4. D. About 300 feet
Show answer
Answer: C. About 32 feet
The manual says air brake lag at 55 mph on dry pavement adds about 32 feet.
From the official CDL manual, section 5.4.4.
20. What is the main danger of a vehicle that has too much brake slack?
1. A. The air compressor will cut out too early
2. B. The spring brakes will come on while driving
3. C. The low air pressure warning will stay on
4. D. It can be very hard to stop
Show answer
Answer: D. It can be very hard to stop
Too much brake slack means the brakes do not apply well, so the vehicle can be very hard to stop.
From the official CDL manual, section 5.3.2.

North Carolina CDL Air Brakes questions

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

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

Is the North Carolina 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. North Carolina uses its own handbook: https://www.ncdot.gov/dmv/license-id/driver-licenses/new-drivers/Documents/commercial-driver-manual.pdf

How much does a CDL permit cost in North Carolina?

CLP fee: $25.50 (listed as Learner's Permit in the manual fee list).

What languages is the North Carolina CDL knowledge test offered in?

The CDL pages do not name the languages for CDL tests and give no English-only rule. For regular license tests NCDMV says tests are offered in different languages and oral tests are available on request, and you can ask for an ASL or language interpreter online.

Sources

https://www.ncdot.gov/dmv/license-id/driver-licenses/new-drivers/Documents/commercial-driver-manual.pdf
https://www.ncdot.gov/dmv/license-id/driver-licenses/commercial/Pages/default.aspx
https://www.ncdot.gov/dmv/license-id/driver-licenses/new-drivers/Pages/driver-license-tests.aspx
Manual sections used in this test: 5.1.1; 5.1.11; 5.1.13; 5.1.14; 5.1.15; 5.1.4; 5.1.7; 5.1.8; 5.2; 5.3.2; 5.3.3; 5.4.3; 5.4.4; 5.4.6

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