Illinois Commercial Driver’s License (CDL)
Air Brakes Endorsement Exam Practice
Questions And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A |
Instant Download Pdf
1. What is the purpose of air brakes on a commercial vehicle?
A. To provide power steering
B. To increase fuel efficiency
C. To safely stop heavy vehicles
D. To improve suspension
Rationale: Air brakes use compressed air to safely and effectively stop
large, heavy vehicles that hydraulic brakes alone cannot handle.
2. What is the first step in performing the air brake system check before
driving?
A. Pump the brake pedal
, B. Check air pressure buildup
C. Release the parking brake
D. Turn on headlights
Rationale: Checking air pressure ensures the system builds up sufficient
pressure for safe braking before operating the vehicle.
3. What happens when the air pressure in the system drops below a safe
level?
A. Engine shuts off
B. Steering becomes difficult
C. Brakes may fail or engage automatically
D. Lights stop working
Rationale: Low air pressure can cause brake failure; safety systems may
automatically apply the brakes to prevent accidents.
4. What device prevents the air brakes from being fully applied if the
system pressure is too low?
A. Brake chamber
B. Slack adjuster
C. Low-pressure warning device
D. Air compressor
Rationale: A low-pressure warning device alerts the driver and prevents
unsafe brake application.
, 5. What is a “dual air brake system”?
A. A system with two compressors
B. A system with hydraulic backup
C. Two separate air brake systems in one vehicle
D. A system with two brake pedals
Rationale: Dual systems have separate circuits (primary and secondary) to
provide redundancy in case one system fails.
6. How do you know if your vehicle has air brakes?
A. Hydraulic fluid check
B. Tire pressure check
C. Check for air brake warning light or system indicator
D. Fuel gauge reading
Rationale: Air brake vehicles will have an indicator or warning light to
identify the system.
7. What is the purpose of a compressor in an air brake system?
A. Pump fuel to the engine
B. Inflate tires
C. Supply air to the brake system reservoir
D. Cool the engine
Rationale: The compressor generates and maintains the air pressure
required to operate the brakes.
, 8. What should the air pressure gauge read before moving a vehicle with
air brakes?
A. 20–40 psi
B. 40–60 psi
C. 90–100 psi (or as specified by manufacturer)
D. 120–140 psi
Rationale: Proper air pressure is needed to ensure brakes operate safely.
9. What is the function of the air tanks in an air brake system?
A. Store fuel
B. Cool the engine
C. Store compressed air for brake operation
D. Provide cabin heating
Rationale: Air tanks act as reservoirs to maintain adequate pressure for
safe braking.
10. What happens if water or oil gets into the air tanks?
A. Brakes work better
B. It can freeze or damage the system, causing brake failure
C. Increases air pressure
D. Decreases fuel consumption
Rationale: Contaminants can freeze or damage components, reducing
braking efficiency.
Air Brakes Endorsement Exam Practice
Questions And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A |
Instant Download Pdf
1. What is the purpose of air brakes on a commercial vehicle?
A. To provide power steering
B. To increase fuel efficiency
C. To safely stop heavy vehicles
D. To improve suspension
Rationale: Air brakes use compressed air to safely and effectively stop
large, heavy vehicles that hydraulic brakes alone cannot handle.
2. What is the first step in performing the air brake system check before
driving?
A. Pump the brake pedal
, B. Check air pressure buildup
C. Release the parking brake
D. Turn on headlights
Rationale: Checking air pressure ensures the system builds up sufficient
pressure for safe braking before operating the vehicle.
3. What happens when the air pressure in the system drops below a safe
level?
A. Engine shuts off
B. Steering becomes difficult
C. Brakes may fail or engage automatically
D. Lights stop working
Rationale: Low air pressure can cause brake failure; safety systems may
automatically apply the brakes to prevent accidents.
4. What device prevents the air brakes from being fully applied if the
system pressure is too low?
A. Brake chamber
B. Slack adjuster
C. Low-pressure warning device
D. Air compressor
Rationale: A low-pressure warning device alerts the driver and prevents
unsafe brake application.
, 5. What is a “dual air brake system”?
A. A system with two compressors
B. A system with hydraulic backup
C. Two separate air brake systems in one vehicle
D. A system with two brake pedals
Rationale: Dual systems have separate circuits (primary and secondary) to
provide redundancy in case one system fails.
6. How do you know if your vehicle has air brakes?
A. Hydraulic fluid check
B. Tire pressure check
C. Check for air brake warning light or system indicator
D. Fuel gauge reading
Rationale: Air brake vehicles will have an indicator or warning light to
identify the system.
7. What is the purpose of a compressor in an air brake system?
A. Pump fuel to the engine
B. Inflate tires
C. Supply air to the brake system reservoir
D. Cool the engine
Rationale: The compressor generates and maintains the air pressure
required to operate the brakes.
, 8. What should the air pressure gauge read before moving a vehicle with
air brakes?
A. 20–40 psi
B. 40–60 psi
C. 90–100 psi (or as specified by manufacturer)
D. 120–140 psi
Rationale: Proper air pressure is needed to ensure brakes operate safely.
9. What is the function of the air tanks in an air brake system?
A. Store fuel
B. Cool the engine
C. Store compressed air for brake operation
D. Provide cabin heating
Rationale: Air tanks act as reservoirs to maintain adequate pressure for
safe braking.
10. What happens if water or oil gets into the air tanks?
A. Brakes work better
B. It can freeze or damage the system, causing brake failure
C. Increases air pressure
D. Decreases fuel consumption
Rationale: Contaminants can freeze or damage components, reducing
braking efficiency.
