25 realistic Air Brakes practice questions for Nevada CDL applicants. Required for: Vehicles equipped with air brake systems. Official test: 25 questions, 20 correct to pass.
Question 1 of 25 · Speed Management
Air brake lag distance at 55 mph on dry pavement adds about:
-
A.
12 feet to stopping distance
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B.
32 feet to stopping distance
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C.
50 feet to stopping distance
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D.
100 feet to stopping distance
Correct answer: B.
Air brake systems have a lag of about 0.4 seconds, adding roughly 32 feet at 55 mph.
Question 2 of 25 · Inspection
How do you test the low pressure warning signal?
-
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 · Foundation Brakes
Brake drums (or discs) must not have cracks longer than:
-
A.
1/4 the width of the friction area
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B.
1/2 the width of the friction area
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C.
3/4 the width of the friction area
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D.
Anything is acceptable
Correct answer: B.
Cracks longer than one-half the width of the friction area are a safety violation.
Question 4 of 25 · ABS
What is the proper procedure for an air brake stop in a vehicle equipped with ABS?
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A.
Pump the brakes
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B.
Press the brake pedal firmly and steadily; let ABS work
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C.
Disengage ABS first
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D.
Apply the parking brake
Correct answer: B.
With ABS, brake firmly and steadily. ABS prevents wheel lockup automatically.
Question 5 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 6 of 25 · Speed Management
Air brake lag is:
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A.
The time required for the brakes to apply after the pedal is pressed
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B.
The amount of free play in the brake pedal
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C.
The distance traveled before the brakes release
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D.
The time to drain air tanks
Correct answer: A.
Lag is the time between pressing the pedal and the brakes actually applying — about 0.4 seconds.
Question 7 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 8 of 25 · Warning Devices
The low air pressure warning device must come on when air pressure in the service tanks falls below:
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A.
80 psi
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B.
60 psi
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C.
50 psi or 1/2 the compressor governor cut-out pressure
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D.
20 psi
Correct answer: C.
Low pressure warnings activate at 60 psi or less (or half the cut-out pressure on older vehicles).
Question 9 of 25 · Tanks
Why must air tanks be drained?
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A.
To remove fuel from the system
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B.
To remove water and compressor oil that can damage the brakes
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C.
To inspect the tanks
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D.
To increase pressure
Correct answer: B.
Water and oil collect in tanks. They damage seals and can freeze in cold weather.
Question 10 of 25 · Gauges
You should know your vehicle is properly equipped with which gauge?
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A.
Two air pressure gauges (or one with two needles) showing pressure in primary and secondary tanks
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B.
A vacuum gauge
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C.
A voltage meter only
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D.
A coolant gauge only
Correct answer: A.
Dual air systems require gauges for both primary and secondary air supplies.
Question 11 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 12 of 25 · Tanks
Air brake equipped vehicles must have:
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A.
Only an emergency brake
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B.
A drain valve in each air tank
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C.
Hydraulic backup
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D.
Disc brakes only
Correct answer: B.
Each air tank has a drain valve to remove water and oil that collect in the tank.
Question 13 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.
Question 14 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 15 of 25 · Compressor
If the air compressor governor is not working properly:
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A.
Air compressor may not maintain enough pressure to safely operate the brakes
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B.
The brakes will work harder
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C.
Brakes may not release at all
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D.
There is no impact on safety
Correct answer: A.
A faulty governor can cause low system pressure or over-pressurization, both unsafe.
Question 16 of 25 · System Basics
Air brakes use compressed air to:
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A.
Lubricate the wheels
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B.
Make the brakes work
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C.
Cool the engine
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D.
Increase fuel pressure
Correct answer: B.
Compressed air is the working fluid that applies the brakes in an air brake system.
Question 17 of 25 · Inspection
How do you know that you have an air leak?
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A.
Pressure drops faster than allowable rate
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B.
You hear hissing
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C.
Both A and B
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D.
The brake pedal feels firm
Correct answer: C.
Pressure dropping faster than allowed and audible hissing both indicate leaks.
Question 18 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 19 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 20 of 25 · Combination Air
What does the trailer hand valve do?
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A.
Operates only the trailer brakes
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B.
Operates both the tractor and trailer brakes
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C.
Engages the parking brakes
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D.
Lowers the landing gear
Correct answer: A.
The hand valve (trolley valve) controls only the trailer service brakes.
Question 21 of 25 · Spring Brakes
What does a "spring brake" mean?
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A.
A brake that operates only in spring weather
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B.
A mechanical brake that uses powerful springs to apply the brake when air pressure is lost
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C.
A specific kind of disc brake
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D.
A backup hydraulic brake
Correct answer: B.
Spring brakes use powerful coil springs to apply the brakes when air pressure is lost.
Question 22 of 25 · Spring Brakes
What does the term "modulating control valve" refer to?
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A.
A valve to regulate engine RPM
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B.
A hand-operated valve that gradually applies the spring brakes
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C.
A device that drains air tanks
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D.
The trailer hand valve
Correct answer: B.
A modulating control valve allows gradual application of spring brakes for emergency or backup use.
Question 23 of 25 · Inspection
When should you check the parking brake?
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A.
Whenever you start a trip
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B.
Once a month
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C.
Only at inspections
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D.
When the brake warning light is on
Correct answer: A.
Test the parking brake every trip — apply the brake and try to move forward gently.
Question 24 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 25 of 25 · Spring Brakes
Modulating control valves do what?
-
A.
Drain water from tanks
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B.
Apply spring brakes gradually using a hand control
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C.
Open the trailer supply line
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D.
Switch to emergency brakes
Correct answer: B.
Modulating valves let you apply the spring brakes gradually rather than all at once.
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 Nevada Department of Motor Vehicles administers this knowledge test as part of its commercial driver license program. To earn the Air Brakes Endorsement on your Nevada CDL, you need to score at least 20 out of 25 on the official version.
Topics covered on this practice test
- Speed Management: 4 questions
- Spring Brakes: 4 questions
- Inspection: 3 questions
- ABS: 2 questions
- Parking: 2 questions
- Tanks: 2 questions
- System Basics: 2 questions
- Combination Air: 2 questions
- Foundation Brakes: 1 question
- Warning Devices: 1 question
- Gauges: 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 Nevada 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.