MI · L (restriction removed) Endorsement

Michigan Air Brakes CDL Practice Test

Below are 25 exam-style questions for the Michigan Air Brakes CDL knowledge test, modeled on the FMCSA-aligned content used by the Michigan Department of State. Try to answer each question on your own before reading the answer key directly under it. The questions and answer choices are shuffled deterministically per state and endorsement, so the order will stay the same on repeat visits — that lets you genuinely measure your improvement.

Heads up: this is a study tool, not a graded exam. Cover the answer with your hand or a sheet of paper for an honest practice run, then re-read the explanations for any questions you missed. Aim for 22 out of 25 or better, three times in a row, before scheduling the real exam.

Question 1 of 25

On a vehicle with dual air brakes, the warning device must come on before pressure in either system drops below:

A 60 psi
B 20 psi
C 40 psi
D Never; only the gauge needs to read it

Correct answer: A

The low-air warning must activate before pressure drops below 60 psi in either circuit.

Question 2 of 25

When applying brakes in an emergency without ABS:

A Use stab braking — apply hard, release when wheels lock, re-apply
B Press as hard as possible and hold
C Use only the parking brake
D Pump rapidly and lightly

Correct answer: A

Stab braking keeps the truck straight in an emergency without ABS. Hard continuous pressure can lock the wheels and cause a jackknife.

Question 3 of 25

Which is true about air storage tanks?

A They never need to be drained
B They must be drained completely once a year
C They drain themselves automatically in all trucks
D They must be drained daily to remove water and oil

Correct answer: D

Most trucks require manual daily draining of each tank. Some have automatic moisture ejectors, but the driver is still responsible.

Question 4 of 25

A driver should never:

A Use the trailer hand valve as a parking brake
B Test the parking brake
C Drain the wet tank
D Make pre-trip inspections

Correct answer: A

The trailer hand valve is not a parking device — see the trailer-hand-valve question. Always set the trailer parking brakes.

Question 5 of 25

Stopping a vehicle with an air-brake failure can sometimes be done by:

A Using the trailer hand valve, then engine braking, then a runaway ramp if needed
B Coasting in neutral
C Honking
D Putting the transmission in reverse

Correct answer: A

In an air-brake failure, the trailer hand valve can still apply the trailer service brakes, then engine braking and a runaway ramp.

Question 6 of 25

Glad-hand seals should be:

A Loose for easy connection
B Free of dirt and damage and properly seated
C Coated with oil
D Removed for inspection

Correct answer: B

Damaged or dirty seals cause leaks. Inspect and clean them as part of the trailer hookup.

Question 7 of 25

You should NOT drain the wet tank when:

A You are about to begin a trip
B The vehicle is in motion
C There is no situation in which draining is wrong
D It is full of moisture

Correct answer: C

Daily draining is a routine task; there is no situation where draining is unsafe (other than while driving).

Question 8 of 25

The proper braking technique on a long downgrade is:

A Apply the parking brake
B Coast in neutral
C Heavy continuous braking
D Light, intermittent braking with engine braking and a low gear

Correct answer: D

Use the proper low gear so engine braking does most of the work; brief, moderate brake applications keep the speed in check.

Question 9 of 25

During the seven-step air-brake check, the final step is to:

A Check tire pressures
B Adjust the slack adjusters
C Pull forward and apply the foot brake to test for stopping
D Drain the wet tank

Correct answer: C

After all stationary tests, perform a moving brake check at low speed to verify the service brakes stop the vehicle.

Question 10 of 25

A brake check ahead of a downgrade should be done:

A Once a year
B At the bottom only
C Before reaching the top, while still on level ground
D In the middle of the descent

Correct answer: C

A brief brake test on level ground at the top reveals problems while you can still stop safely.

Question 11 of 25

Cross-leakage between primary and secondary brake systems is:

A Required by federal law
B Caused by overuse
C A serious defect that can prevent backup braking
D A normal feature

Correct answer: C

Each circuit must remain independent so a failure in one still leaves the other working.

Question 12 of 25

You should test the service brakes by:

A Listening to the air gauge
B At about 5 mph, applying the brake firmly and feeling for pulling, sticking, or unusual feel
C Pumping the brakes
D Driving at 30 mph and slamming on the brakes

Correct answer: B

A low-speed brake test catches sticking, pulling, or weak brakes before you build up speed.

Question 13 of 25

Brake drums in good condition will:

A Be free of cracks longer than half the width of the friction area
B Have small cracks
C Be glowing red after stops
D Be coated with oil

Correct answer: A

Cracks longer than half the friction area or any visible heat checks usually fail inspection.

Question 14 of 25

Each axle group on an air-brake-equipped vehicle has its own:

A Air compressor
B Drive shaft
C Engine
D Set of brake chambers

Correct answer: D

Each axle group has its own brake chambers fed by the air system; one compressor supplies all of them.

Question 15 of 25

A common cause of an air-brake skid is:

A Neither of the above
B Both of the above
C Locking the wheels by braking too hard
D Driving too fast for conditions

Correct answer: B

Skids result when the wheel locks and the tire loses traction. Speed and over-application are both common contributors.

Question 16 of 25

Spring brakes do NOT replace:

A The tail lights
B The headlights
C The horn
D The service brakes for normal stops

Correct answer: D

Spring brakes are for parking and emergency only — never for normal service braking.

Question 17 of 25

When approaching a long downgrade, you should:

A Skip the brake test
B Coast in neutral
C Test the brakes at the bottom
D Test the brakes by lightly applying them at the top

Correct answer: D

A light brake application at the top tests for pulling or weakness before the descent puts heat into the system.

Question 18 of 25

Air-brake hoses should:

A Be wrapped in tape
B Have at least 5 splices each
C Be coiled tightly under the truck
D Show no signs of damage, leaks, or excessive wear

Correct answer: D

Damaged or chafed hoses are a common air-brake defect and a frequent out-of-service citation.

Question 19 of 25

When a vehicle is hooked to a trailer, the air system must include:

A Only a safety chain
B Only an electrical connector
C One additional reservoir for the trailer brakes
D Service line and emergency line, with glad-hand connectors

Correct answer: D

Air goes through service and emergency (supply) lines to the trailer, with glad-hand connectors and color-coded couplers.

Question 20 of 25

Slack adjusters should be checked because:

A They are decorative
B They affect engine performance
C Out-of-adjustment slack adjusters can result in brakes that do not work properly
D They control trailer height

Correct answer: C

Slack adjusters convert pushrod motion into braking force. Out-of-adjustment slack adjusters reduce braking ability and are a common out-of-service item.

Question 21 of 25

A common reason for compressor failure to keep up is:

A A clogged air filter or worn compressor
B A broken governor
C All of the above
D A leak in the brake system

Correct answer: C

Any of these causes can prevent the compressor from maintaining cut-out pressure.

Question 22 of 25

Anti-lock braking systems (ABS) on air-brake vehicles:

A Are required only on hazmat trailers
B Replace foundation brakes
C Help prevent wheel lockup but do not necessarily shorten stopping distance
D Are optional and rarely installed

Correct answer: C

ABS helps the driver maintain steering control by preventing wheel lockup. It does not necessarily reduce stopping distance.

Question 23 of 25

Front-wheel brakes are required on commercial vehicles because:

A Federal law mandates them as decorative
B They look balanced
C They reduce stopping distance significantly without normally causing skids on dry pavement
D They make steering easier

Correct answer: C

Front brakes provide a large share of stopping force and modern vehicles are designed so they do not cause front-wheel skids on dry pavement.

Question 24 of 25

Air dryers are used in air-brake systems to:

A Cool the air before it enters the brake chambers
B Remove moisture and contaminants from the compressed air
C Increase pressure
D Replace governors

Correct answer: B

Dryers reduce moisture in the air system, helping prevent corrosion, ice in winter, and contamination.

Question 25 of 25

When you press the brake pedal, brake pressure is:

A Built up from zero by the pedal
B Received from a separate accumulator
C Created by the pedal mechanically
D Released from the storage tanks

Correct answer: D

Pressing the pedal releases stored air from the tanks into the brake chambers; the pedal does not generate pressure itself.

Study tips for the Michigan Air Brakes exam

The Air Brakes portion of the Michigan CDL exam is graded out of the bank of questions the Michigan Department of State draws from each year. While the exact bank is not published, every question is sourced from the Air Brakes chapter of the Michigan CDL handbook, which itself is derived from the FMCSA Model Commercial Driver's License Manual. That means studying our practice tests, reading the corresponding handbook chapter, and re-reading the parts you got wrong is genuinely the most efficient route to a first-time pass.

Most successful applicants follow a simple cycle: take the practice test cold, write down every question you missed, open the matching chapter of the official Michigan handbook, re-read the section that contains the right answer, then re-take the practice test 24 to 48 hours later. The 24-hour delay matters — sleep is when your brain commits new information to long-term memory, and CDL knowledge questions reward that kind of consolidated learning rather than cramming.

Pay particular attention to questions that include qualifier words like always, never, only, primary, or most. CDL test writers love to flip the right answer with a single qualifier. When two answer choices look almost identical, pay attention to the verb (is it must, should, or may?) and to any numbers (14 days, 100 air miles, 8 hours, 70/8 split). On endorsement tests in particular, watch for trick framing where a true statement about a different endorsement is offered as the "correct" answer to a question that is actually about Air Brakes.

Test-day logistics matter too. Bring photo ID, your Social Security card or birth certificate, your medical examiner's certificate (DOT card), and proof of state residency if you haven't already submitted those documents. The Michigan Department of State will not let you sit for the knowledge exam without your documentation, and most offices charge an additional fee for re-attempts. Arrive early — the wait at most CDL testing offices runs 30 to 60 minutes — and silence your phone before the exam begins.

Finally, keep your General Knowledge fundamentals sharp even when you're focused on the Air Brakes exam. Many states administer multiple knowledge tests in a single sitting, and questions on weight definitions (GVWR, GCWR, GAWR), stopping distance, and the pre-trip inspection routine show up across endorsements. If you're unsure on the basics, sit a fresh Michigan General Knowledge practice test before scheduling the real exam.

Next steps

Missed more than four questions? Re-read the Air Brakes study guide and the matching chapter in the official Michigan CDL handbook. Then come back and re-take the test. Once you can score 22 of 25 or higher on three runs in a row, you're in good shape to schedule the real exam at your local Michigan Department of State office.

Already comfortable with this endorsement? Drill another: MI General Knowledge · MI Combination Vehicles · MI Hazardous Materials · MI Passenger · MI School Bus · MI Tank Vehicle · MI Doubles / Triples

New to the CDL process in Michigan? Read How to apply for a CDL in Michigan for the document checklist and step-by-step timeline.