ND · L (restriction removed) Endorsement

North Dakota Air Brakes CDL Practice Test

Below are 25 exam-style questions for the North Dakota Air Brakes CDL knowledge test, modeled on the FMCSA-aligned content used by the North Dakota Department of Transportation. 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

Slack adjusters should be checked because:

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

Correct answer: D

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 2 of 25

Air pressure should normally build from 50 to 90 psi within:

A It does not matter
B Less than 30 seconds
C 10 minutes
D About 3 minutes in dual systems

Correct answer: D

Dual air systems should build from 50 to 90 psi within about 3 minutes at idle.

Question 3 of 25

Spring brakes do NOT replace:

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

Correct answer: C

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

Question 4 of 25

The air compressor is driven by:

A The engine, by belts or directly geared
B The exhaust system
C The transmission
D The electrical system

Correct answer: A

Compressors are typically engine-driven, either by a belt or direct gearing, so air pressure builds whenever the engine runs.

Question 5 of 25

When approaching a long downgrade, you should:

A Test the brakes at the bottom
B Skip the brake test
C Coast in neutral
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 6 of 25

You should not over-tighten a glad-hand because:

A It violates federal weight law
B It will reduce engine power
C It is bad luck
D It can damage the rubber seals

Correct answer: D

Over-tightening crushes the seals. The connection should be firm but not forced.

Question 7 of 25

In a dual system, normal cut-in pressure is approximately:

A 85 psi
B 125 psi
C 60 psi
D 40 psi

Correct answer: C

Cut-in is usually around 100 psi but cut-out is around 125 psi. Cut-in below 60 psi indicates a problem in many systems.

Question 8 of 25

When you press the brake pedal, brake pressure is:

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

Correct answer: A

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

Question 9 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 Pump rapidly and lightly
D Use only the parking brake

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 10 of 25

When applying brakes in an emergency with ABS:

A Press as hard as possible and hold
B Release the brakes immediately
C Pump rapidly
D Stab the brakes

Correct answer: A

With ABS, full pressure works because the system pulses for you, allowing maximum braking while preserving steering.

Question 11 of 25

A brake check ahead of a downgrade should be done:

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

Correct answer: D

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

Question 12 of 25

A common reason for compressor failure to keep up is:

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

Correct answer: B

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

Question 13 of 25

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

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

Correct answer: C

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

Question 14 of 25

If the ABS warning light comes on while driving, you should:

A Pump the brakes hard
B Immediately stop on the side of the road
C Continue driving — you still have normal brakes — and have the system checked at the next opportunity
D Disconnect the trailer

Correct answer: C

A failed ABS system reverts to normal braking. Get it repaired but you can complete the trip.

Question 15 of 25

You should test the service brakes by:

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

Correct answer: C

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

Question 16 of 25

Air dryers are used in air-brake systems to:

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

Correct answer: B

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

Question 17 of 25

Why should you NOT use the trailer hand valve to hold a parked combination vehicle?

A It will activate the spring brakes
B It is illegal
C It only works while the engine is running
D Air leaks could cause the brakes to release and let the vehicle roll

Correct answer: D

The hand valve relies on continuous air pressure. A slow leak releases the brakes and the vehicle rolls.

Question 18 of 25

After making the initial brake application, the air-pressure drop should not exceed:

A 2-3 psi
B 5 psi
C 10 psi
D 1 psi

Correct answer: A

A small initial drop is normal as the system equalizes — but excessive drop indicates a leak.

Question 19 of 25

The air compressor governor controls:

A Engine RPM
B Brake pad wear
C Coolant temperature
D When the air compressor will pump air into the storage tanks

Correct answer: D

The governor cuts the compressor in (start pumping) at low pressure and cuts it out (stop pumping) at high pressure to maintain a working range.

Question 20 of 25

If air pressure drops in the emergency line:

A Nothing happens
B Trailer spring brakes apply automatically
C Tractor brakes apply
D Trailer service brakes apply

Correct answer: B

Loss of supply-line pressure is the failsafe that triggers the trailer's spring brakes.

Question 21 of 25

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

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

Correct answer: B

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

Question 22 of 25

A leaking air system on a parked truck is dangerous because:

A The fuel will leak
B It can wake the driver
C When pressure drops far enough, spring brakes apply suddenly and the vehicle becomes unmovable
D The engine will not start

Correct answer: C

A bigger problem is en route: if a slow leak goes unnoticed and pressure drops below the spring-brake set point, the brakes apply on the road.

Question 23 of 25

A common practice during a long brake-recharge wait is to:

A Allow the system to reach operating pressure before driving
B Check the brake light visibility
C Disable the warning lamp
D Drain the wet tank

Correct answer: A

Always wait for full operating pressure (typically around 120 psi) before moving the vehicle.

Question 24 of 25

Spring-brake pop-out occurs at approximately:

A 20 to 45 psi
B 60 to 80 psi
C 90 to 100 psi
D 0 to 10 psi

Correct answer: A

Pop-out is typically between 20 and 45 psi, varying by manufacturer.

Question 25 of 25

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

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

Correct answer: B

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

Study tips for the North Dakota Air Brakes exam

The Air Brakes portion of the North Dakota CDL exam is graded out of the bank of questions the North Dakota Department of Transportation draws from each year. While the exact bank is not published, every question is sourced from the Air Brakes chapter of the North Dakota 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 North Dakota 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 North Dakota Department of Transportation 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 North Dakota 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 North Dakota 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 North Dakota Department of Transportation office.

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

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