Free Michigan DMV CDL — Air Brakes Practice Test 2026
The Michigan CDL — Air Brakes knowledge test has 25 questions, and you need 20 correct (80%) to pass. Practice free with questions written from the official Michigan 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 Michigan written test
The Michigan CDL — Air Brakes knowledge test has 25 questions; you need 20 correct (80%) to pass.
Based on the official Michigan 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 Michigan practice questions.
How to pass the first time
- Read the official Michigan 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.
Michigan CDL — Air Brakes test — frequently asked questions
How many questions are on the Michigan CDL — Air Brakes test?
The Michigan 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 Michigan 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 Michigan 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 Michigan 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 Michigan 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 Michigan driver handbook, practice by topic to target weak areas, and finish with full-length tests until you consistently pass.
Other Michigan practice tests
Take the CDL — Air Brakes test in another state
Every Michigan question is written from the official Michigan 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
Michigan CDL — Air Brakes questions with answers
20 sample questions from the Michigan 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. With the engine off and the system fully charged, a single vehicle's air pressure should drop by no more than how much in one minute?
Correct answer: 2 psi
For a static leak check on a single vehicle, the loss should stay under 2 psi per minute (under 3 psi per minute for a combination) with the parking brake released.
Source: Michigan CDL Manual — Section 5.3.3: Final Air Brake Check
2. On a typical air brake vehicle, the low air pressure warning you can see must switch on before tank pressure drops below what level?
Correct answer: 60 psi
A visible low-pressure warning is required and must come on before the pressure in the tanks falls under 60 psi (older vehicles may instead use half the governor cut-out pressure).
Source: Michigan CDL Manual — Section 5.1.11: Low Air Pressure Warning
3. If one half of a dual air brake system loses most of its pressure, what happens?
Correct answer: Either the front or the rear brakes won't work fully, so stopping takes longer
With one half very low, the brakes it controls (front or rear) will not work fully, which lengthens your stopping distance; stop safely and have the system repaired.
Source: Michigan CDL Manual — Section 5.2: Dual Air Brake
4. Which statement best describes what antilock brakes actually do for you?
Correct answer: They keep the wheels from locking during hard braking so you stay in control, though they may not shorten stopping distance
ABS is an add-on to your normal brakes that activates only when the wheels are about to lock; it helps you hold control during hard braking but does not necessarily shorten how far it takes to stop.
Source: Michigan CDL Manual — Section 5.1.16: Antilock Braking Systems (ABS)
5. Vehicles built since which year come with automatic slack adjusters?
Correct answer: 1994
Every vehicle manufactured since 1994 has automatic slack adjusters; they still must be inspected even though they adjust themselves during full brake applications.
Source: Michigan CDL Manual — Section 5.3.2: Walk-Around Inspection
6. When should you skip setting the parking brakes and use wheel chocks instead?
Correct answer: When the brakes are very hot from a steep grade, or very wet in freezing temperatures
Very hot brakes can be damaged by the parking brake, and wet brakes in freezing weather can freeze and trap the vehicle; in those cases let them cool or dry and chock the wheels.
Source: Michigan CDL Manual — Section 5.4.8: Parking Brakes
7. Why is it important to empty the air tanks of the moisture that collects inside them?
Correct answer: Collected water can freeze in cold weather and knock out the brakes
Compressed air carries water and a little compressor oil that settle at the bottom of the tank; in cold weather that water can turn to ice and cause the brakes to fail, so the tanks must be drained.
Source: Michigan CDL Manual — Section 5.1.4: Air Tank Drains
8. On a trailer equipped with ABS, where is the yellow malfunction lamp located?
Correct answer: On the left side, at the front or rear corner
Tractors, trucks, and buses show the ABS malfunction lamp on the instrument panel, while trailers place the yellow lamp on the left side, either at the front or the rear corner.
Source: Michigan CDL Manual — Section 5.1.16: Antilock Braking Systems (ABS)
9. For a vehicle with air brakes, total stopping distance is made up of which factors?
Correct answer: Perception, reaction, brake lag, and braking distance
Air brakes add a brake-lag component, so the total is perception distance plus reaction distance plus brake-lag distance plus braking distance.
Source: Michigan CDL Manual — Section 5.4.4: Stopping Distance
10. Suppose the low-pressure warning activates while you are driving. What is the safest thing to do?
Correct answer: Stop and safely park as soon as possible, because there may be an air leak
Treat the warning as a possible leak: stop and park while there is still enough air to use the foot brakes, since controlled braking is only possible while air remains in the tanks.
Source: Michigan CDL Manual — Section 5.4.7: Low Air Pressure
11. According to the manual, what is the defect turned up most often during roadside inspections?
Correct answer: Brakes that are out of adjustment
Out-of-adjustment brakes are named as the problem found most frequently in roadside inspections, which is why checking the slack adjusters matters.
Source: Michigan CDL Manual — Section 5.3.2: Walk-Around Inspection
12. 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
With the spring brakes set, adding pedal (air) force stacks the two forces together and can damage the brakes, so it is best to never do it.
Source: Michigan CDL Manual — Section 5.1.15: Parking Brake Controls
13. What most directly causes brake fade on a long downgrade?
Correct answer: Excessive heat from overusing the service brakes
Leaning on the service brakes instead of the engine's braking effect overheats them; the heat changes the linings chemically and expands the drums, which reduces braking force.
Source: Michigan CDL Manual — Section 5.4.5: Brake Fading or Failure
14. How does an air brake vehicle switch on its brake lights to warn drivers behind it?
Correct answer: An electric switch triggered by air pressure when you apply the brakes
An air-pressure-operated electric switch closes when you press the brakes, lighting the stop lamps so following drivers know you are slowing.
Source: Michigan CDL Manual — Section 5.1.12: Stop Light Switch
15. What does "brake lag" refer to on a vehicle with air brakes?
Correct answer: The short delay before the brakes work because the air must travel through the lines
Unlike hydraulic brakes that act at once, air brakes need a moment (about half a second or more) for the air to travel through the lines and reach the brakes, adding a lag not present on cars.
Source: Michigan CDL Manual — Section 5.4.4: Stopping Distance
16. On a tractor or straight truck, the spring brakes will come fully on once air pressure drops into which range?
Correct answer: 20 to 45 psi (often 20 to 30 psi)
As tank pressure falls into roughly the 20-to-45 psi band, most often 20 to 30 psi, the springs come fully on; you should not wait for that to happen while driving.
Source: Michigan CDL Manual — Section 5.1.14: Spring Brakes
17. Air-braked truck tractors are required to have antilock brakes if they were built on or after which date?
Correct answer: March 1, 1997
Truck tractors with air brakes made on or after March 1, 1997 must have ABS; other air-braked vehicles such as trucks, buses, trailers, and converter dollies carry the requirement from March 1, 1998.
Source: Michigan CDL Manual — Section 5.1.16: Antilock Braking Systems (ABS)
18. What must you always do before leaving your vehicle unattended?
Correct answer: Apply the parking brakes or chock the wheels
An unattended vehicle can roll away and cause injury or damage, so always set the parking brakes or chock the wheels before you walk away.
Source: Michigan CDL Manual — Section 5.4.8: Parking Brakes
19. The safety relief valve on the first air tank is normally set to open at about what pressure?
Correct answer: About 150 psi
Installed on the first reservoir the compressor feeds, the safety valve guards against over-pressurization and typically releases near 150 psi.
Source: Michigan CDL Manual — Section 5.1.6: Safety Valve
20. On a vehicle with a dual air brake system, how is tank pressure shown?
Correct answer: A separate gauge for each half, or one gauge with two needles
Because a dual system has two independent halves, each half gets its own supply gauge, or the two readings share a single gauge with two needles.
Source: Michigan CDL Manual — Section 5.1.9: Supply Pressure Gauges