Pennsylvania CDL Air Brakes Practice Test

The Pennsylvania 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 (Pennsylvania does not publish its own number).

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 Pennsylvania 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.

Pennsylvania CDL permit facts

What	What Pennsylvania says	Source
Air Brakes pass mark	At least 80%. This is the federal minimum (49 CFR 383.135); Pennsylvania does not publish its own number.	Official page
Air Brakes test questions	25 (Fact sheet row is 'L/Z Air Brake Restriction Removal' (25 questions))	Official page
CLP fee (photo fee, one permit)	$15.50 photo fee, plus $6.00 for each endorsement or restriction removal (no fee for the school bus endorsement). Add $5 for each additional commercial permit on the fee chart.	Official page
CLP validity	The permit is valid for one year from the date the Knowledge Test Authorization (KTA) is issued.	Official page
Test languages	PennDOT offers knowledge tests in multiple languages, in written and audio format. The hazmat knowledge test is English only. The test language list is not published on the pages checked.	Official page

20 question Air Brakes practice test

1. Your safe speed on a downgrade is 40 mph. You brake when you reach 40 mph. At what speed do you release the brakes?
1. A. 39 mph
2. B. 30 mph
3. C. 20 mph
4. D. 35 mph
Show answer
Answer: D. 35 mph
The manual's example slows from the 40 mph safe speed to 35 mph, about five mph below, then releases.
From the official CDL manual, section 5.4.6.
2. At about what tank pressure does the governor stop the compressor from pumping air?
1. A. 125 psi
2. B. 100 psi
3. C. 150 psi
4. D. 55 psi
Show answer
Answer: A. 125 psi
The cut-out level is around 125 psi.
From the official CDL manual, section 5.1.2.
3. 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.
4. 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.
5. 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.
6. You are using the controlled braking method. How should you move the steering wheel?
1. A. Make large, quick turns
2. B. Hold the wheel tightly and never move it
3. C. Turn it back and forth
4. D. Keep the movements very small
Show answer
Answer: D. Keep the movements very small
Keep steering wheel movements very small during controlled braking.
From the official CDL manual, section 5.4.3.
7. When should the low air warning light and buzzer shut off on a dual air brake vehicle?
1. A. When either system reaches 55 psi
2. B. When both reach the manufacturer's value, above 55 psi
3. C. When the primary system alone reaches 20 psi
4. D. Only when both systems reach exactly 125 psi
Show answer
Answer: B. When both reach the manufacturer's value, above 55 psi
The signals shut off once both systems rise to the manufacturer's value, which must be greater than 55 psi.
From the official CDL manual, section 5.2.
8. Why is manual adjustment of an automatic slack adjuster dangerous?
1. A. It voids the vehicle's registration
2. B. It always makes the brakes lock up
3. C. It can give a false sense of security about the brakes
4. D. It makes the air tanks leak
Show answer
Answer: C. It can give a false sense of security about the brakes
The manual says it may give the driver a false sense of security.
From the official CDL manual, section 5.3.2.
9. Your truck has automatic slack adjusters, which adjust themselves. Do you still need to check them?
1. A. No, they never need to be checked
2. B. Yes, they must still be checked
3. C. Only if the low air warning comes on
4. D. Only after the brakes have been rebuilt
Show answer
Answer: B. Yes, they must still be checked
Automatic slack adjusters adjust themselves, but the manual says they must still be checked.
From the official CDL manual, section 5.3.2.
10. 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.
11. An automatic adjuster's pushrod stroke is over the legal limit. What does this usually show?
1. A. The tires are worn
2. B. A mechanical problem or a bad installation
3. C. The tank has too much air
4. D. The brakes are working better
Show answer
Answer: B. A mechanical problem or a bad installation
The manual says it indicates a mechanical problem or an improper installation.
From the official CDL manual, section 5.3.2.
12. When is it acceptable to manually adjust an automatic slack adjuster?
1. A. Every morning as part of the pre-trip
2. B. Any time the brakes feel a little soft
3. C. Whenever the push rod stroke is past the limit, as a permanent fix
4. D. Only as a temporary fix in an emergency
Show answer
Answer: D. Only as a temporary fix in an emergency
Manual adjustment of an automatic adjuster is only a temporary measure for an emergency, because the real problem remains.
From the official CDL manual, section 5.3.2.
13. 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.
14. A heavily loaded vehicle's spring brakes come on after an air loss. Why does it take a long distance to stop?
1. A. The spring brakes do not work on all axles
2. B. The air tanks must refill before the brakes can work
3. C. The compressor stops pumping at that point
4. D. The service brakes lock the wheels at once
Show answer
Answer: A. The spring brakes do not work on all axles
Spring brakes do not work on all axles, so a heavily loaded vehicle takes a long distance to stop.
From the official CDL manual, section 5.4.7.
15. Some buses have a separate air tank tied to dual parking control valves. What is it for?
1. A. Releasing the spring brakes to move in an emergency
2. B. Filling the service brake tanks more quickly
3. C. Holding the spring brakes on while the bus is parked
4. D. Running the low air pressure warning signal
Show answer
Answer: A. Releasing the spring brakes to move in an emergency
The separate tank can release the spring brakes so the vehicle can be moved in an emergency.
From the official CDL manual, section 5.1.15.
16. The compressor stops working. How much braking can the full air tanks still give you?
1. A. Enough for the brakes to be used several times
2. B. Enough for one hard stop and no more
3. C. None at all, so the brakes fail at once
4. D. Enough to keep braking all day without it
Show answer
Answer: A. Enough for the brakes to be used several times
Tanks hold enough air for several brake applications even without the compressor.
From the official CDL manual, section 5.1.3.
17. Typically, what is the pressure of a fully charged air system at the start of the leakage test?
1. A. 125 psi
2. B. 60 psi
3. C. 85 psi
4. D. 45 psi
Show answer
Answer: A. 125 psi
The manual says a fully charged system is typically 125 psi.
From the official CDL manual, section 5.3.3.
18. The low pressure warning does not work on a single-circuit air system. What could happen?
1. A. You could lose air without knowing, then get sudden emergency braking
2. B. The compressor would stop building air
3. C. The service brakes would apply more gently
4. D. The governor would cut out at 100 psi
Show answer
Answer: A. You could lose air without knowing, then get sudden emergency braking
Without a warning you would not know pressure is falling, and a single-circuit system could suddenly apply emergency braking.
From the official CDL manual, section 5.3.3.
19. When is controlled braking possible with air brakes?
1. A. Only after the spring brakes apply
2. B. Only on dry roads
3. C. Only while enough air remains in the tanks
4. D. At any air pressure
Show answer
Answer: C. Only while enough air remains in the tanks
Controlled braking works only while enough air is in the tanks.
From the official CDL manual, section 5.4.7.
20. Your vehicle has no ABS and you brake hard on a slippery road. What happens if the steering wheels lock up?
1. A. The spring brakes release
2. B. You lose steering control
3. C. The air tanks refill faster
4. D. The vehicle stops in a shorter distance
Show answer
Answer: B. You lose steering control
When steering wheels lock up, you lose steering control.
From the official CDL manual, section 5.4.2.

Pennsylvania CDL Air Brakes questions

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

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

Is the Pennsylvania 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. Pennsylvania uses its own handbook: https://www.pa.gov/content/dam/copapwp-pagov/en/penndot/documents/public/dvspubsforms/bdl/bdl-manuals/commercial-drivers-manual/pub223.pdf

How much does a CDL permit cost in Pennsylvania?

CLP fee (photo fee, one permit): $15.50 photo fee, plus $6.00 for each endorsement or restriction removal (no fee for the school bus endorsement). Add $5 for each additional commercial permit on the fee chart..

What languages is the Pennsylvania CDL knowledge test offered in?

PennDOT offers knowledge tests in multiple languages, in written and audio format. The hazmat knowledge test is English only. The test language list is not published on the pages checked.

Sources

https://www.ecfr.gov/current/title-49/section-383.135
https://www.pa.gov/content/dam/copapwp-pagov/en/penndot/documents/public/dvspubsforms/bdl/bdl-fact-sheets/fs-cdl.pdf
https://www.pa.gov/content/dam/copapwp-pagov/en/penndot/documents/public/dvspubsforms/bdl/bdl-form/dl-31cd.pdf
https://www.pa.gov/content/dam/copapwp-pagov/en/penndot/documents/public/dvspubsforms/bdl/bdl-manuals/commercial-drivers-manual/pub223.pdf
Manual sections used in this test: 5.1.15; 5.1.16; 5.1.2; 5.1.3; 5.1.8; 5.2; 5.3.2; 5.3.3; 5.4.2; 5.4.3; 5.4.6; 5.4.7

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