Tennessee CDL Air Brakes Practice Test

The Tennessee CDL Air Brakes test is a multiple-choice knowledge test you take for your commercial learner's permit. You need at least 80% to pass. That's the federal minimum in 49 CFR 383.135 (Tennessee does not publish its own number).

Last updated Oct 16, 2026. FirstTry CDL is a CDL permit test prep site by Hive Asset Group, LLC.

By Scott Wilder, Editor

Last reviewed against the Tennessee CDL manual on October 16, 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.

Tennessee CDL permit facts

What	What Tennessee says	Source
Air Brakes pass mark	At least 80%. This is the federal minimum (49 CFR 383.135); Tennessee does not publish its own number.	Official page
Class A CLP fee	$14.00 total ($8.00 per year for 1 year plus $6.00 application fee)	Official page
Class B or C CLP fee	$13.00 total ($7.00 per year for 1 year plus $6.00 application fee)	Official page
CLP validity	365 days. If you do not convert the CLP to a CDL before it expires, all knowledge and skills tests become null and void.	Official page
Knowledge test retest rule	If you fail a knowledge test, you may retake it the next day. Applicants caught cheating are told by the DSC manager when they may retest.	Official page
Test languages	The manual says you may take a paper test or have the computer read the test to you in English, and to ask the DSC about other testing options. The official sources do not list other test languages or state an English-only rule.	Official page

20 question Air Brakes practice test

1. In the proper low gear on a downgrade, how hard should you apply the brakes?
1. A. Just hard enough to feel a definite slowdown
2. B. As hard as you can without locking the wheels
3. C. As lightly as possible, and keep them applied all the way down
4. D. Only enough to turn on the brake lights
Show answer
Answer: A. Just hard enough to feel a definite slowdown
The proper technique is to apply the brakes just hard enough to feel a definite slowdown.
From the official CDL manual, section 5.4.6.
2. How should you inspect a vehicle that has air brakes?
1. A. Check the air brakes only at the end of the trip
2. B. Check only the air brake parts and skip the rest
3. C. Use a special air brake method instead of the seven steps
4. D. Use the seven-step method and add the air brake checks
Show answer
Answer: D. Use the seven-step method and add the air brake checks
The manual says to use the basic seven-step procedure, with more things to inspect.
From the official CDL manual, section 5.3.
3. Why do most heavy-duty vehicles use dual air brake systems?
1. A. To make the brakes cheaper
2. B. For safety
3. C. To save fuel
4. D. To make the brake pedal lighter
Show answer
Answer: B. For safety
The manual says most heavy-duty vehicles use dual air brake systems for safety.
From the official CDL manual, section 5.2.
4. How does a dual air brake system show tank pressure?
1. A. One gauge for each half, or one gauge with two needles
2. B. One needle that shows the average of both halves
3. C. A single gauge for the primary half only
4. D. A warning light that shows the total pressure
Show answer
Answer: A. One gauge for each half, or one gauge with two needles
A dual system has a gauge for each half, or one gauge with two needles.
From the official CDL manual, section 5.1.9.
5. What can ABS help you do in a hard stop?
1. A. Steer around an obstacle while braking
2. B. Always stop in a shorter distance
3. C. Follow closer to the vehicle ahead
4. D. Skip the use of engine braking on grades
Show answer
Answer: A. Steer around an obstacle while braking
With ABS you may or may not stop faster, but you should be able to steer around an obstacle while braking.
From the official CDL manual, section 5.4.2.
6. Your vehicle has no automatic air tank drains. Why must you drain the tanks at the end of each working day?
1. A. To lower pressure so the governor cuts in sooner
2. B. To keep the tanks from overfilling above 125 psi
3. C. To keep the spring brakes from coming on overnight
4. D. To remove moisture and oil, or the brakes could fail
Show answer
Answer: D. To remove moisture and oil, or the brakes could fail
Draining removes moisture and oil from the tanks; otherwise the brakes could fail.
From the official CDL manual, section 5.4.8.
7. 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.
8. What does the safety valve protect the air brake system from?
1. A. Too little pressure
2. B. Water in the tanks
3. C. Worn brake linings
4. D. Too much pressure
Show answer
Answer: D. Too much pressure
The safety valve protects the tank and the system from too much pressure.
From the official CDL manual, section 5.1.6.
9. Why should you not use the parking brakes when they are very wet in freezing temperatures?
1. A. They will release by themselves overnight
2. B. The air tanks will lose all their pressure
3. C. They can freeze so the vehicle cannot move
4. D. The brake lag will become longer
Show answer
Answer: C. They can freeze so the vehicle cannot move
Very wet brakes can freeze when the parking brakes are set in freezing temperatures, and the vehicle cannot move.
From the official CDL manual, section 5.4.8.
10. You are about to pull on the slack adjusters to check them. How should the vehicle be set up first?
1. A. On level ground, wheels chocked, parking brakes released
2. B. On level ground, wheels chocked, parking brakes applied
3. C. On a slight slope, wheels not chocked, parking brakes released
4. D. Engine running at fast idle, parking brakes applied
Show answer
Answer: A. On level ground, wheels chocked, parking brakes released
You chock the wheels on level ground and release the parking brakes so the adjusters can move.
From the official CDL manual, section 5.3.2.
11. An older trailer may have ABS but it is hard to tell. What can you look for under the vehicle?
1. A. The electronic control unit and wheel speed sensor wires
2. B. A second air compressor
3. C. An alcohol evaporator
4. D. A front brake limiting valve
Show answer
Answer: A. The electronic control unit and wheel speed sensor wires
Look for the electronic control unit (ECU) and wheel speed sensor wires from the back of the brakes.
From the official CDL manual, section 5.1.16.
12. 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.
13. You run the engine at fast idle for the governor test. What should the gauge do when the governor cuts out?
1. A. Fall quickly to zero
2. B. Keep rising until the safety valve opens
3. C. Jump back down to the cut-in pressure
4. D. Stop rising
Show answer
Answer: D. Stop rising
When the governor cuts out the compressor, the gauge readings stop rising.
From the official CDL manual, section 5.3.3.
14. As you fan off pressure on a straight truck, what should the parking brake valve do at the specified pressure?
1. A. Close and pop out, so the spring brakes come on
2. B. Stay pushed in until pressure reaches zero
3. C. Pop out at about 100 psi
4. D. Push in harder to hold the brakes off
Show answer
Answer: A. Close and pop out, so the spring brakes come on
When pressure falls to the manufacturer's specification, the parking brake valve should pop out and apply the spring brakes.
From the official CDL manual, section 5.3.3.
15. 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.
16. When you check brake drums, linings, and hoses, what must be true of the mechanical parts?
1. A. They must be painted
2. B. They must be in place and not broken or missing
3. C. They may be loose if they are clean
4. D. They may be missing if the brakes still work
Show answer
Answer: B. They must be in place and not broken or missing
The manual says mechanical parts must be in place, not broken or missing.
From the official CDL manual, section 5.3.2.
17. What does the air compressor governor control?
1. A. How hard the brake shoes press on the drum
2. B. When the spring brakes release
3. C. How much alcohol enters the system
4. D. When the compressor pumps air into the tanks
Show answer
Answer: D. When the compressor pumps air into the tanks
The governor decides when the compressor pumps air and when it stops.
From the official CDL manual, section 5.1.2.
18. Which problem is the most common one found in roadside inspections of air brake vehicles?
1. A. Cracked air tanks
2. B. Broken compressor governors
3. C. Brakes that are out of adjustment
4. D. Missing alcohol in the evaporator
Show answer
Answer: C. Brakes that are out of adjustment
The manual says out-of-adjustment brakes are the most common problem found in roadside inspections.
From the official CDL manual, section 5.3.2.
19. How often must you drain manual air tanks yourself?
1. A. Once a week
2. B. Only in cold weather
3. C. Only when pressure falls below 100 psi
4. D. At the end of each day of driving
Show answer
Answer: D. At the end of each day of driving
Manual tanks must be drained at the end of each day of driving.
From the official CDL manual, section 5.1.4.
20. During the walk-around, which brake lining condition is a defect?
1. A. Covered with a light layer of brake dust
2. B. Showing normal wear but still thick enough
3. C. Loose or soaked with oil or grease
4. D. Slightly darker than the brake drum
Show answer
Answer: C. Loose or soaked with oil or grease
The manual says linings must not be loose, soaked with oil or grease, or dangerously thin.
From the official CDL manual, section 5.3.2.

Tennessee CDL Air Brakes questions

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

You need at least 80% to pass. That is the federal minimum in 49 CFR 383.135. Tennessee does not publish its own number.

Is the Tennessee 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. Tennessee uses its own handbook: https://www.tn.gov/content/dam/tn/safety/documents/CDL_Manual_May2022.pdf

How much does a CDL permit cost in Tennessee?

Class A CLP fee: $14.00 total ($8.00 per year for 1 year plus $6.00 application fee).

What languages is the Tennessee CDL knowledge test offered in?

The manual says you may take a paper test or have the computer read the test to you in English, and to ask the DSC about other testing options. The official sources do not list other test languages or state an English-only rule.

Sources

https://www.ecfr.gov/current/title-49/section-383.135
https://www.tn.gov/safety/driver-services/helpful-information/fees.html
https://www.tn.gov/content/dam/tn/safety/documents/CDL_Manual_May2022.pdf
Manual sections used in this test: 5.1.14; 5.1.16; 5.1.2; 5.1.4; 5.1.6; 5.1.9; 5.2; 5.3; 5.3.2; 5.3.3; 5.4.2; 5.4.6; 5.4.8

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