CDL Air Brakes (L) Endorsement Practice
Exam Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What is the purpose of the air brake system on a commercial vehicle?
a. To make the vehicle go faster
b. To reduce tire wear
c. To stop and hold the vehicle safely
d. To control steering
Air brakes provide the force needed to stop and hold large vehicles
safely, which mechanical brakes alone cannot do.
2. How often should you check your air pressure gauge during a trip?
a. Only before starting the vehicle
b. Regularly while driving
c. Only when the brakes feel weak
d. Only at the end of the trip
, Monitoring air pressure regularly ensures that the brakes remain
operational and prevents sudden failures.
3. What should you do if the air pressure drops below the safe level
while driving?
a. Keep driving until you reach a service station
b. Pump the brakes harder
c. Stop safely and use emergency procedures
d. Shift to a lower gear
Air pressure that is too low can cause brake failure. Stopping safely is
essential to prevent accidents.
4. At what pressure does the air compressor governor typically cut out?
a. 80 psi
b. 120-140 psi
c. 60-80 psi
d. 150-160 psi
The governor stops the compressor from pumping air when pressure
reaches 120-140 psi to prevent over-pressurization.
5. What does the "low air pressure warning" signal in most vehicles?
a. Brake fluid is low
b. Air pressure has dropped below 60 psi
c. Tire pressure is low
d. Parking brake is applied
, A warning is triggered when air pressure is too low to safely operate
brakes, typically below 60 psi.
6. What is the function of a spring brake?
a. Assist steering
b. Increase engine power
c. Serve as a parking brake and emergency brake
d. Control trailer brakes
Spring brakes apply automatically when air pressure is lost or when
the parking brake is engaged, providing a fail-safe.
7. What is the first step in performing an air brake pre-trip inspection?
a. Check tires
b. Build air pressure and check for leaks
c. Check mirrors
d. Test turn signals
Ensuring the air system is charged and leak-free is the first step
before operating the vehicle.
8. How can you check the air compressor governor cut-in and cut-out
pressures?
a. By listening to the engine
b. By observing the tachometer
c. By watching the air pressure gauge
d. By checking the oil level
, The air pressure gauge shows when the compressor starts (cut-in)
and stops (cut-out) pumping.
9. What is a “wigwag” in an air brake system?
a. Steering mechanism
b. Fuel indicator
c. Low air pressure warning device
d. Air filter
A wigwag mechanically signals when air pressure falls below a safe
level, usually below 60 psi.
10. When should you perform the applied brake test?
a. Only when parked
b. At high speeds
c. During the pre-trip inspection before moving
d. After braking in traffic
This test ensures that brakes apply properly before the vehicle
moves.
11. How do you check the slack adjuster on a S-cam brake?
a. Measure tire tread
b. Listen for air leaks
c. Pull it by hand with brakes released; it should move less than 1
inch
d. Check fluid level
Exam Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What is the purpose of the air brake system on a commercial vehicle?
a. To make the vehicle go faster
b. To reduce tire wear
c. To stop and hold the vehicle safely
d. To control steering
Air brakes provide the force needed to stop and hold large vehicles
safely, which mechanical brakes alone cannot do.
2. How often should you check your air pressure gauge during a trip?
a. Only before starting the vehicle
b. Regularly while driving
c. Only when the brakes feel weak
d. Only at the end of the trip
, Monitoring air pressure regularly ensures that the brakes remain
operational and prevents sudden failures.
3. What should you do if the air pressure drops below the safe level
while driving?
a. Keep driving until you reach a service station
b. Pump the brakes harder
c. Stop safely and use emergency procedures
d. Shift to a lower gear
Air pressure that is too low can cause brake failure. Stopping safely is
essential to prevent accidents.
4. At what pressure does the air compressor governor typically cut out?
a. 80 psi
b. 120-140 psi
c. 60-80 psi
d. 150-160 psi
The governor stops the compressor from pumping air when pressure
reaches 120-140 psi to prevent over-pressurization.
5. What does the "low air pressure warning" signal in most vehicles?
a. Brake fluid is low
b. Air pressure has dropped below 60 psi
c. Tire pressure is low
d. Parking brake is applied
, A warning is triggered when air pressure is too low to safely operate
brakes, typically below 60 psi.
6. What is the function of a spring brake?
a. Assist steering
b. Increase engine power
c. Serve as a parking brake and emergency brake
d. Control trailer brakes
Spring brakes apply automatically when air pressure is lost or when
the parking brake is engaged, providing a fail-safe.
7. What is the first step in performing an air brake pre-trip inspection?
a. Check tires
b. Build air pressure and check for leaks
c. Check mirrors
d. Test turn signals
Ensuring the air system is charged and leak-free is the first step
before operating the vehicle.
8. How can you check the air compressor governor cut-in and cut-out
pressures?
a. By listening to the engine
b. By observing the tachometer
c. By watching the air pressure gauge
d. By checking the oil level
, The air pressure gauge shows when the compressor starts (cut-in)
and stops (cut-out) pumping.
9. What is a “wigwag” in an air brake system?
a. Steering mechanism
b. Fuel indicator
c. Low air pressure warning device
d. Air filter
A wigwag mechanically signals when air pressure falls below a safe
level, usually below 60 psi.
10. When should you perform the applied brake test?
a. Only when parked
b. At high speeds
c. During the pre-trip inspection before moving
d. After braking in traffic
This test ensures that brakes apply properly before the vehicle
moves.
11. How do you check the slack adjuster on a S-cam brake?
a. Measure tire tread
b. Listen for air leaks
c. Pull it by hand with brakes released; it should move less than 1
inch
d. Check fluid level
