DMV CDL Air Brakes Endorsement Exam
Questions With Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
Download Pdf
1. What is the main purpose of an air brake system on a commercial
vehicle?
A. To increase engine power
B. To reduce fuel consumption
C. To use compressed air to apply braking force
D. To control steering stability
Rationale: Air brake systems use compressed air to activate brake
components, allowing heavy vehicles to stop safely and reliably under
load.*
2. What happens when air pressure is applied to the brake chamber?
A. The wheels accelerate
B. The pushrod extends and applies the brakes
,C. The brake shoes detach
D. The air is released automatically
Rationale: Air pressure moves a diaphragm in the brake chamber,
causing the pushrod to extend and activate the foundation brakes.*
3. What is the purpose of the air compressor in an air brake system?
A. Store air for emergencies
B. Pump and maintain air pressure in the system
C. Release excess air pressure
D. Cool the braking system
Rationale: The air compressor continuously supplies compressed air
needed for brake operation and system pressure maintenance.*
4. What is the governor in an air brake system responsible for?
A. Controlling steering
B. Regulating air compressor cut-in and cut-out pressure
C. Activating parking brakes
D. Cooling brake drums
Rationale: The governor controls when the compressor builds air and
when it stops to maintain proper system pressure.*
,5. What is the typical cut-out pressure for most air brake systems?
A. 50 psi
B. 90 psi
C. 120–140 psi
D. 200 psi
Rationale: Most systems are designed to stop compressor operation
around 120–140 psi to prevent over-pressurization.*
6. What is the purpose of the air storage tanks?
A. Cool compressed air
B. Filter engine oil
C. Store compressed air for braking use
D. Increase braking speed
Rationale: Air tanks store compressed air so it is available instantly
when the brakes are applied.*
7. What is the safety valve in an air brake system designed to do?
A. Increase brake force
B. Release excess air pressure if it becomes too high
, C. Stop air flow completely
D. Drain moisture from the system
Rationale: The safety valve prevents system damage by releasing air if
pressure exceeds safe limits.*
8. What is the purpose of the brake pedal (treadle valve)?
A. Releases parking brakes only
B. Controls how much air is sent to the brake chambers
C. Measures air pressure
D. Stores air for braking
Rationale: The brake pedal regulates air pressure sent to the brakes,
controlling braking intensity.*
9. What is brake lag?
A. Time it takes engine to start
B. Delay between pressing brake pedal and brake application
C. Brake overheating
D. Air compressor delay
Rationale: Brake lag is the slight delay caused by air traveling through
the system.*
Questions With Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
Download Pdf
1. What is the main purpose of an air brake system on a commercial
vehicle?
A. To increase engine power
B. To reduce fuel consumption
C. To use compressed air to apply braking force
D. To control steering stability
Rationale: Air brake systems use compressed air to activate brake
components, allowing heavy vehicles to stop safely and reliably under
load.*
2. What happens when air pressure is applied to the brake chamber?
A. The wheels accelerate
B. The pushrod extends and applies the brakes
,C. The brake shoes detach
D. The air is released automatically
Rationale: Air pressure moves a diaphragm in the brake chamber,
causing the pushrod to extend and activate the foundation brakes.*
3. What is the purpose of the air compressor in an air brake system?
A. Store air for emergencies
B. Pump and maintain air pressure in the system
C. Release excess air pressure
D. Cool the braking system
Rationale: The air compressor continuously supplies compressed air
needed for brake operation and system pressure maintenance.*
4. What is the governor in an air brake system responsible for?
A. Controlling steering
B. Regulating air compressor cut-in and cut-out pressure
C. Activating parking brakes
D. Cooling brake drums
Rationale: The governor controls when the compressor builds air and
when it stops to maintain proper system pressure.*
,5. What is the typical cut-out pressure for most air brake systems?
A. 50 psi
B. 90 psi
C. 120–140 psi
D. 200 psi
Rationale: Most systems are designed to stop compressor operation
around 120–140 psi to prevent over-pressurization.*
6. What is the purpose of the air storage tanks?
A. Cool compressed air
B. Filter engine oil
C. Store compressed air for braking use
D. Increase braking speed
Rationale: Air tanks store compressed air so it is available instantly
when the brakes are applied.*
7. What is the safety valve in an air brake system designed to do?
A. Increase brake force
B. Release excess air pressure if it becomes too high
, C. Stop air flow completely
D. Drain moisture from the system
Rationale: The safety valve prevents system damage by releasing air if
pressure exceeds safe limits.*
8. What is the purpose of the brake pedal (treadle valve)?
A. Releases parking brakes only
B. Controls how much air is sent to the brake chambers
C. Measures air pressure
D. Stores air for braking
Rationale: The brake pedal regulates air pressure sent to the brakes,
controlling braking intensity.*
9. What is brake lag?
A. Time it takes engine to start
B. Delay between pressing brake pedal and brake application
C. Brake overheating
D. Air compressor delay
Rationale: Brake lag is the slight delay caused by air traveling through
the system.*
