25 realistic Air Brakes practice questions for New Mexico CDL applicants. Required for: Vehicles equipped with air brake systems. Official test: 25 questions, 20 correct to pass.
Question 1 of 25 · System Basics
Which of the following is NOT in the air brake system?
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A.
Brake chambers
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B.
Slack adjusters
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C.
S-cam
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D.
Hydraulic master cylinder
Correct answer: D.
Hydraulic master cylinders are part of hydraulic systems, not air brake systems.
Question 2 of 25 · Inspection
How do you test the low pressure warning signal?
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A.
With the engine off, pump the brake pedal until the signal activates (must come on at 60 psi or above)
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B.
Drive the vehicle to lose pressure
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C.
Open the air tank drain valve briefly
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D.
Push the parking brake control
Correct answer: A.
Pump the brake to lower pressure; warning must come on at 60 psi or higher.
Question 3 of 25 · Emergency Maneuvers
Stab braking includes which of these steps?
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A.
Apply brakes fully, release when wheels lock, reapply when wheels begin rolling
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B.
Apply brakes lightly until they fade
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C.
Pump the brakes rapidly
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D.
Apply the parking brake repeatedly
Correct answer: A.
Stab braking: full application, release on lockup, reapply when wheels turn again.
Question 4 of 25 · Parking
You should never use the trailer hand valve to park because:
-
A.
It is not strong enough
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B.
The air could leak out, releasing the brakes
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C.
It only applies the front brakes
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D.
It is not connected to the trailer
Correct answer: B.
If air leaks out, the brakes release. Always use the parking brake to park.
Question 5 of 25 · Inspection
Which of the following must be checked before operating an air-braked vehicle?
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A.
Low air pressure warning signal
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B.
Spring brakes set automatically
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C.
Air leakage rate
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D.
All of the above
Correct answer: D.
All of these are required pre-trip air brake checks.
Question 6 of 25 · Speed Management
Total stopping distance for an air-braked vehicle is made up of:
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A.
Perception distance + reaction distance + brake lag distance + braking distance
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B.
Just the braking distance
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C.
Reaction distance only
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D.
Brake lag distance only
Correct answer: A.
It is the sum of perception distance, reaction distance, brake lag distance, and braking distance.
Question 7 of 25 · ABS
Which is true about ABS?
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A.
It activates only on dry roads
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B.
It activates only when wheels are about to lock during heavy braking
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C.
It is the same as anti-skid
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D.
It eliminates the need for skid recovery
Correct answer: B.
ABS activates only when wheels are about to lock; otherwise the brake system operates normally.
Question 8 of 25 · ABS
If the ABS warning light comes on, you should:
-
A.
Stop driving immediately
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B.
Continue, knowing brakes still work — but ABS may not
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C.
Pump the brakes constantly
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D.
Engage the trailer hand valve
Correct answer: B.
You still have normal braking; only the ABS function may be off. Get it fixed soon.
Question 9 of 25 · System Basics
Which of these is NOT a part of the basic air brake system?
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A.
Air compressor
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B.
Air storage tanks
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C.
Hydraulic master cylinder
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D.
Foot brake valve
Correct answer: C.
Hydraulic master cylinders belong to hydraulic brake systems, not air brake systems.
Question 10 of 25 · Parking
On a tractor with no trailer attached, the tractor parking brake control:
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A.
Will lock and unlock the front brakes
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B.
Will set or release the spring brakes on the tractor
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C.
Has no function
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D.
Operates only the trailer brakes
Correct answer: B.
The yellow diamond control sets and releases the tractor parking (spring) brakes.
Question 11 of 25 · Parking
Why should you use chocks?
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A.
When parking on a hill
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B.
On level ground when leaving the vehicle
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C.
Whenever brakes might fail or it's required by company policy or law
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D.
All of the above
Correct answer: D.
Chocks should be used when required to prevent vehicle movement.
Question 12 of 25 · Speed Management
Which of these statements is true about brake fading?
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A.
Resting brakes does not bring back braking power
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B.
Brake fade is caused by drums getting too hot
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C.
Brake fade only affects new vehicles
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D.
Brake fade only happens with disc brakes
Correct answer: B.
Brake fade results from overheated drums or discs reducing friction and braking ability.
Question 13 of 25 · Combination Air
What component prevents air pressure loss in case of a leak between the tractor and trailer?
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A.
Tractor protection valve
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B.
Air dryer
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C.
Foot brake valve
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D.
Modulating valve
Correct answer: A.
The tractor protection valve closes off the trailer air supply during a leak, protecting tractor air.
Question 14 of 25 · Combination Air
When should the trailer brake hand valve be used?
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A.
To park the trailer
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B.
To test the trailer brakes only
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C.
To stop the entire combination
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D.
Never to keep the vehicle from rolling
Correct answer: B.
Use it only to test trailer brakes. Never use it to park or as a service brake during normal stops.
Question 15 of 25 · Spring Brakes
If your vehicle has dual parking control valves, you can use pressure from a separate tank to:
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A.
Charge the trailer brakes
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B.
Release the spring brakes to move a short distance if the main system loses air
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C.
Operate the steering
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D.
Power the air horn
Correct answer: B.
Dual parking control valves let you temporarily release spring brakes from a backup tank.
Question 16 of 25 · Spring Brakes
Spring brakes:
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A.
Are released by air pressure
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B.
Are applied by air pressure
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C.
Should be tested by pumping the brake pedal
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D.
Are only on the trailer
Correct answer: A.
Spring brakes are held off (released) by air pressure. When pressure drops, the springs apply the brakes.
Question 17 of 25 · Gauges
What gauge tells you the air pressure being delivered to the brakes?
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A.
Application pressure gauge
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B.
Supply pressure gauge
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C.
Speedometer
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D.
Tachometer
Correct answer: A.
The application gauge shows pressure being applied to the brakes when the pedal is pressed.
Question 18 of 25 · Speed Management
Brake fade results from:
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A.
Oversized brakes
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B.
Excessive heat from prolonged braking
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C.
Too much air pressure
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D.
Cold weather
Correct answer: B.
Brake fade is caused by overheating brakes that lose stopping power.
Question 19 of 25 · Foundation Brakes
When checking the slack adjuster on S-cam brakes, the slack adjuster should not move more than:
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A.
1/2 inch
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B.
1 inch
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C.
About 1 inch where the push rod attaches to it
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D.
2 inches
Correct answer: C.
When pulled by hand, the slack adjuster shouldn't move more than about an inch where the push rod attaches.
Question 20 of 25 · Spring Brakes
What happens if the air pressure drops to between 20 and 45 psi?
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A.
Nothing happens
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B.
The compressor cuts in
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C.
Spring brakes apply automatically
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D.
The trailer is released
Correct answer: C.
Spring brakes typically apply automatically in this range, stopping the vehicle.
Question 21 of 25 · System Basics
Air brake systems combine three different braking systems. They are:
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A.
Service, parking, and emergency brakes
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B.
Hydraulic, parking, and emergency brakes
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C.
Front, rear, and trailer brakes
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D.
Disc, drum, and parking brakes
Correct answer: A.
The three are: the service brake, the parking brake, and the emergency brake.
Question 22 of 25 · ABS
Which is correct about ABS-equipped vehicles?
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A.
You should never use ABS
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B.
ABS works only at high speeds
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C.
You should drive the same way as without ABS, except brake firmly without pumping in emergencies
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D.
ABS makes stopping distance shorter
Correct answer: C.
Drive normally; in emergencies, brake firmly and let ABS prevent lockup. ABS doesn't shorten stopping distance.
Question 23 of 25 · Parking
When parking a tractor-trailer with spring brakes:
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A.
Use the trailer hand valve only
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B.
Use the parking brake only — do not push the brake pedal down to hold the vehicle
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C.
Press the foot brake and then engage the parking brake
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D.
Set both brakes simultaneously
Correct answer: B.
Don't push the pedal down because it will cause damage. Set the parking brakes only.
Question 24 of 25 · Compressor
What is the purpose of a one-way check valve?
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A.
Allow air to flow in one direction
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B.
Allow water to drain
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C.
Prevent the trailer from moving
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D.
Increase pressure in the supply tank
Correct answer: A.
It permits airflow in one direction only — protecting the system if the compressor fails.
Question 25 of 25 · Spring Brakes
Where are spring brakes typically NOT found?
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A.
Front steering axle
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B.
Drive axles
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C.
Trailer axles
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D.
Tractor rear axles
Correct answer: A.
Spring brakes are found on drive axles and trailer axles, not normally on the steering axle.
About the Air Brakes Test
The Air Brakes test covers air brake system parts (compressor, governor, reservoirs, drain valves, alcohol evaporator, safety valve, brake pedal, foundation brakes), dual air brake systems, inspecting air brakes, using air brakes (normal stops, emergency stops, parking brakes), and proper procedures for braking on downgrades. If you fail or skip the Air Brakes test, your CDL is restricted to vehicles without full air brake systems.
The New Mexico Motor Vehicle Division administers this knowledge test as part of its commercial driver license program. To earn the Air Brakes Endorsement on your New Mexico CDL, you need to score at least 20 out of 25 on the official version.
Topics covered on this practice test
- Parking: 4 questions
- Spring Brakes: 4 questions
- System Basics: 3 questions
- Speed Management: 3 questions
- ABS: 3 questions
- Inspection: 2 questions
- Combination Air: 2 questions
- Emergency Maneuvers: 1 question
- Gauges: 1 question
- Foundation Brakes: 1 question
- Compressor: 1 question
How to use this practice test
- Read each question carefully. CDL questions are written precisely — small wording differences matter.
- Click "Show Answers & Explanations" only after answering every question. Don't peek mid-test.
- Read the explanation for every question, even ones you got right. The reasoning is more important than the answer.
- Repeat the test until you score 100%. The questions are deterministic per state, so you can track your improvement over multiple sessions.
- Move on to the other endorsement tests for New Mexico until you're ready for the official exam.
Tips specific to the Air Brakes test
Air Brakes questions test your ability to identify components, follow inspection sequences, and respond to system failures. Memorize the cut-in and cut-out pressures, the low-pressure warning thresholds, the pressure ranges at which spring brakes apply, and the maximum allowable air-loss rates. Many questions have nearly-identical wording, so precision matters.