CDL Air Brakes Exam Questions
And Correct Answers (Verified
Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What is the main purpose of an air brake system?
A. Increase engine power
B. Use compressed air to apply braking force
C. Replace steering system
D. Reduce fuel consumption
Answer: B
Rationale: Air brake systems use compressed air to activate brake
components.
2. What happens when air pressure in the system drops too low?
A. Brakes become stronger
B. Spring brakes automatically engage
C. Vehicle accelerates
D. Engine shuts off
Answer: B
Rationale: Spring brakes engage when air pressure is insufficient.
3. What is the function of an air compressor?
A. Stores air
B. Produces compressed air
C. Releases brake fluid
D. Controls steering
Answer: B
Rationale: The compressor generates compressed air for the system.
,4. What is the purpose of an air storage tank?
A. Cool engine
B. Store compressed air
C. Measure speed
D. Control fuel
Answer: B
Rationale: Tanks store compressed air for braking use.
5. What is the purpose of a governor in an air brake system?
A. Controls air compressor cut-in and cut-out pressure
B. Controls steering
C. Releases brake shoes
D. Measures tire pressure
Answer: A
Rationale: The governor regulates compressor operation.
6. What is “air pressure build-up time”?
A. Time to start engine
B. Time needed to increase air pressure to operating level
C. Time to stop vehicle
D. Time to change tires
Answer: B
Rationale: It measures how quickly air pressure builds.
7. What is the minimum safe air pressure for most air brake systems before
driving?
A. 20 psi
B. 50 psi
C. 100 psi or more
D. 5 psi
Answer: C
Rationale: Vehicles typically require at least 100 psi to operate safely.
8. What is the purpose of an air dryer?
A. Heat engine oil
B. Remove moisture from compressed air
C. Increase braking force
, D. Control steering
Answer: B
Rationale: Moisture removal prevents freezing and corrosion.
9. What does the brake pedal control in an air brake system?
A. Fuel flow
B. Air pressure sent to brake chambers
C. Engine speed
D. Transmission shift
Answer: B
Rationale: Pedal regulates air pressure to brakes.
10.What happens when the brake pedal is pressed harder?
A. Less air pressure is sent
B. More air pressure is applied
C. Engine stops
D. Steering locks
Answer: B
Rationale: More pedal force increases braking pressure.
11.What is the purpose of slack adjusters?
A. Control fuel
B. Adjust brake shoe clearance
C. Increase engine speed
D. Cool brakes
Answer: B
Rationale: They maintain proper brake adjustment.
12.What is “brake fade”?
A. Increase in braking power
B. Loss of braking efficiency due to heat
C. Air pressure increase
D. Engine overheating
Answer: B
Rationale: Heat reduces brake effectiveness.
13.What is the purpose of the low air pressure warning system?
A. Increase speed
And Correct Answers (Verified
Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What is the main purpose of an air brake system?
A. Increase engine power
B. Use compressed air to apply braking force
C. Replace steering system
D. Reduce fuel consumption
Answer: B
Rationale: Air brake systems use compressed air to activate brake
components.
2. What happens when air pressure in the system drops too low?
A. Brakes become stronger
B. Spring brakes automatically engage
C. Vehicle accelerates
D. Engine shuts off
Answer: B
Rationale: Spring brakes engage when air pressure is insufficient.
3. What is the function of an air compressor?
A. Stores air
B. Produces compressed air
C. Releases brake fluid
D. Controls steering
Answer: B
Rationale: The compressor generates compressed air for the system.
,4. What is the purpose of an air storage tank?
A. Cool engine
B. Store compressed air
C. Measure speed
D. Control fuel
Answer: B
Rationale: Tanks store compressed air for braking use.
5. What is the purpose of a governor in an air brake system?
A. Controls air compressor cut-in and cut-out pressure
B. Controls steering
C. Releases brake shoes
D. Measures tire pressure
Answer: A
Rationale: The governor regulates compressor operation.
6. What is “air pressure build-up time”?
A. Time to start engine
B. Time needed to increase air pressure to operating level
C. Time to stop vehicle
D. Time to change tires
Answer: B
Rationale: It measures how quickly air pressure builds.
7. What is the minimum safe air pressure for most air brake systems before
driving?
A. 20 psi
B. 50 psi
C. 100 psi or more
D. 5 psi
Answer: C
Rationale: Vehicles typically require at least 100 psi to operate safely.
8. What is the purpose of an air dryer?
A. Heat engine oil
B. Remove moisture from compressed air
C. Increase braking force
, D. Control steering
Answer: B
Rationale: Moisture removal prevents freezing and corrosion.
9. What does the brake pedal control in an air brake system?
A. Fuel flow
B. Air pressure sent to brake chambers
C. Engine speed
D. Transmission shift
Answer: B
Rationale: Pedal regulates air pressure to brakes.
10.What happens when the brake pedal is pressed harder?
A. Less air pressure is sent
B. More air pressure is applied
C. Engine stops
D. Steering locks
Answer: B
Rationale: More pedal force increases braking pressure.
11.What is the purpose of slack adjusters?
A. Control fuel
B. Adjust brake shoe clearance
C. Increase engine speed
D. Cool brakes
Answer: B
Rationale: They maintain proper brake adjustment.
12.What is “brake fade”?
A. Increase in braking power
B. Loss of braking efficiency due to heat
C. Air pressure increase
D. Engine overheating
Answer: B
Rationale: Heat reduces brake effectiveness.
13.What is the purpose of the low air pressure warning system?
A. Increase speed
