Free Tennessee DMV CDL — Air Brakes Practice Test 2026
The Tennessee CDL — Air Brakes knowledge test has ~25 questions, and you need ~20 correct (80%) to pass. Practice free with questions written from the official Tennessee driver handbook — every one has a clear explanation, and you can retake as often as you like with no sign-up.
Content reviewed against official driver handbooks · August 12, 2026
What's on the Tennessee written test
The Tennessee CDL — Air Brakes knowledge test has ~25 questions; you need ~20 correct (80%) to pass.
Based on the official Tennessee exam format — always confirm current details with your state DMV.
Practice by topic
Focus on one area at a time — each topic has its own set of Tennessee practice questions.
How to pass the first time
- Read the official Tennessee driver handbook at least once before test day.
- Practice by topic to find your weak spots, then fix them.
- Take full-length practice tests until you pass comfortably every time.
- Read every explanation — understanding beats memorizing.
Tennessee CDL — Air Brakes test — frequently asked questions
How many questions are on the Tennessee CDL — Air Brakes test?
The Tennessee CDL — Air Brakes knowledge test has ~25 questions, and you need ~20 correct (80%) to pass. Our practice tests mirror that format.
How many questions can I miss on the Tennessee CDL — Air Brakes test?
You can miss up to ~5 of the ~25 questions and still pass — you need ~20 correct, which is 80%.
Can I retake the practice test?
Yes — practice as often as you like, completely free. The questions and answer choices are shuffled each time.
Can I take the Tennessee practice test in Spanish?
Yes. Every question here is available in English and Spanish — switch languages anytime. Many states also offer the real knowledge test in languages other than English; confirm what Tennessee offers with your DMV.
Can I practice on my phone?
Yes. The practice tests work in any mobile or desktop browser — no app or sign-up needed — so you can study anywhere.
Are these the real DMV test questions?
No. Our questions are original, written from the current official Tennessee driver handbook to match the real test's topics and style. We are not affiliated with any DMV or government agency.
What's the best way to study?
Read the Tennessee driver handbook, practice by topic to target weak areas, and finish with full-length tests until you consistently pass.
Other Tennessee practice tests
Take the CDL — Air Brakes test in another state
Every Tennessee question is written from the official Tennessee driver handbook and checked against its current edition. DMV Test Free is a free, independent study resource — not affiliated with any DMV or government agency. About DMV Test Free
Tennessee CDL — Air Brakes questions with answers
20 sample questions from the Tennessee CDL — Air Brakes question bank — each with the correct answer, a short explanation, and the section of the official handbook it comes from.
Show all 20 questions with answers
1. On a newer air brake vehicle, how do you set the parking brakes?
Correct answer: Pull out the yellow diamond-shaped knob
You apply the parking (spring) brakes by pulling out the yellow, diamond-shaped push-pull control knob, and you release them by pushing it back in.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.1.15 Parking Brake Controls
2. With the engine off and the foot brake fully applied, what air loss rate is acceptable for a single vehicle over one minute?
Correct answer: No more than three psi in one minute
With the parking brake released and the foot brake held down, a single vehicle's pressure should not fall more than three psi in one minute (a combination vehicle is allowed four psi).
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.3.3 Final Air Brake Check
3. While driving, the low-pressure warning suddenly comes on. What is your safest move?
Correct answer: Stop and safely park as soon as possible
Controlled braking is only possible while enough air remains, and the spring brakes come on around 20 to 45 psi, so you should stop and safely park as soon as possible while you still have foot brakes.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.4.7 Low Air Pressure
4. What happens to a brake drum if the brakes are used so hard and so long that they overheat?
Correct answer: Too much heat can cause the brakes to stop working
Friction at the drum creates heat, and although drums can absorb a lot of it, too much heat can make the brakes quit working.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.1.8 Foundation Brakes
5. What must you always do before leaving your vehicle unattended?
Correct answer: Apply the parking brakes or chock the wheels
You should never leave the vehicle unattended without setting the parking brakes or chocking the wheels, or it could roll away and cause injury and damage.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.4.8 Parking Brakes
6. At about what pressure does the governor let the compressor start pumping again (the cut-in pressure)?
Correct answer: About 100 psi
Once tank pressure drops to the cut-in point of roughly 100 psi, the governor lets the compressor start building air again.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.1.2 Air Compressor Governor
7. On a tractor or straight truck, spring brakes typically come fully on when the air pressure falls into what range?
Correct answer: 20 to 45 psi
The spring brakes on a tractor or straight truck engage fully once pressure drops into the 20 to 45 psi range, most often somewhere between 20 and 30 psi.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.1.14 Spring Brakes
8. Which factors are added together to make up the total stopping distance for an air brake vehicle?
Correct answer: Perception, reaction, brake lag, and braking distance
Total stopping distance for air brakes is perception distance plus reaction distance plus brake lag distance plus braking distance, the brake lag being the extra factor air brakes add.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.4.4 Stopping Distance
9. When making a normal stop with a manual transmission, when should you push in the clutch?
Correct answer: Only once engine speed has fallen close to idle
For a smooth normal stop with a manual transmission, wait to push in the clutch until the engine rpm has dropped close to idle, then select a starting gear.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.4.1 Normal Stops
10. An air brake setup is really a combination of three braking systems. Which trio is correct?
Correct answer: Service, parking, and emergency brakes
Air brakes bundle three systems together: the service brakes for everyday stops, the parking brakes for holding the rig in place, and the emergency brakes that can halt the vehicle if a failure happens.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - overview
11. How is the "stab braking" method performed in an emergency?
Correct answer: Apply fully, release when wheels lock, then apply fully again once they roll
In stab braking you press the brakes all the way, release them when the wheels lock, and reapply fully once the wheels start rolling again.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.4.3 Emergency Stops
12. On a long, steep downgrade, the braking effect of the service brakes should be treated as what?
Correct answer: Only a supplement to the engine's braking effect
On a long or steep downgrade the service brakes are only a supplement to the engine's braking effect; you should already be in a low gear before relying on them.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.4.6 Proper Braking Technique
13. How do you test that the parking brake will hold?
Correct answer: Set it, then in a low gear gently try to ease forward against it
To check the parking brake, come to a stop, apply it, and in a low gear ease the vehicle forward against it to be sure it holds.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.3.3 Final Air Brake Check
14. How do you test the service brakes as part of the final check?
Correct answer: Roll ahead at roughly five mph, then press the brakes hard, noting any pulling or delay
With normal pressure built and the parking brake off, ease the vehicle forward at roughly five mph, then press the brakes firmly and watch for pulling to one side, an unusual feel, or a slow stop.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.3.3 Final Air Brake Check
15. What is "controlled braking" during an emergency stop?
Correct answer: Braking as hard as possible without letting the wheels lock, using tiny steering inputs
Controlled braking means pressing as firmly as possible short of locking the wheels, while keeping steering inputs tiny; if a wheel locks or you must steer more, release and reapply.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.4.3 Emergency Stops
16. On the application pressure gauge, needing more and more pressure to hold the same speed is a sign of what, and what should you do?
Correct answer: The brakes are fading, so slow down and use a lower gear
Rising application pressure to keep a steady speed means the brakes are fading; the correct response is to slow down and shift to a lower gear.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.1.10 Application Pressure Gauge
17. Why should you avoid pressing the brake pedal while the spring brakes are already applied?
Correct answer: The combined spring and air forces could damage the brakes
Pushing the pedal with the spring brakes on can damage the brakes, because the springs and the air pressure combine to overload them.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.1.15 Parking Brake Controls
18. A visible low air pressure warning must come on before tank pressure drops below what level on most vehicles?
Correct answer: 55 psi
Vehicles with air brakes must give a warning you can see before the tank pressure falls below 55 psi.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.1.11 Low Air Pressure Warning
19. When using stab braking, why must you wait before re-applying the brakes after releasing them?
Correct answer: The wheels can take up to a second to start rolling, and you must let them
After you let off, the wheels may need as much as a second to start turning again; re-applying before they roll keeps the vehicle from straightening out.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.4.3 Emergency Stops
20. What causes brake fade from overheating?
Correct answer: Too much heat changing the lining and expanding the drums
Excessive heat from overusing the brakes causes chemical changes in the lining that cut friction and makes the drums expand, so the shoes must travel farther and press with less force.
Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.4.5 Brake Fading or Failure