Exam Questions And Correct Answers

CDL Air Brakes (L) Endorsement Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the purpose of the air brake system on a commercial vehicle?
• To make the vehicle go faster
• To reduce tire wear
• To stop and hold the vehicle safely
• To control steering

Air brakes provide the force needed to stop and hold large vehicles safely, which mechanical brakes alone cannot do.

• How often should you check your air pressure gauge during a trip?
• Only before starting the vehicle
• Regularly while driving
• Only when the brakes feel weak
• Only at the end of the trip 1 / 4

Monitoring air pressure regularly ensures that the brakes remain operational and prevents sudden failures.

• What should you do if the air pressure drops below the safe level

while driving?

• Keep driving until you reach a service station
• Pump the brakes harder
• Stop safely and use emergency procedures
• Shift to a lower gear

Air pressure that is too low can cause brake failure. Stopping safely is essential to prevent accidents.

• At what pressure does the air compressor governor typically cut out?
• 80 psi
• 120-140 psi
• 60-80 psi
• 150-160 psi

The governor stops the compressor from pumping air when pressure reaches 120-140 psi to prevent over-pressurization.

• What does the "low air pressure warning" signal in most vehicles?
• Brake fluid is low
• Air pressure has dropped below 60 psi
• Tire pressure is low
• Parking brake is applied 2 / 4

A warning is triggered when air pressure is too low to safely operate brakes, typically below 60 psi.

• What is the function of a spring brake?
• Assist steering
• Increase engine power
• Serve as a parking brake and emergency brake
• Control trailer brakes

Spring brakes apply automatically when air pressure is lost or when the parking brake is engaged, providing a fail-safe.

• What is the first step in performing an air brake pre-trip inspection?
• Check tires
• Build air pressure and check for leaks
• Check mirrors
• Test turn signals

Ensuring the air system is charged and leak-free is the first step before operating the vehicle.

• How can you check the air compressor governor cut-in and cut-out

pressures?

• By listening to the engine
• By observing the tachometer
• By watching the air pressure gauge
• By checking the oil level 3 / 4

The air pressure gauge shows when the compressor starts (cut-in) and stops (cut-out) pumping.

• What is a “wigwag” in an air brake system?
• Steering mechanism
• Fuel indicator
• Low air pressure warning device
• Air filter

A wigwag mechanically signals when air pressure falls below a safe level, usually below 60 psi.

• When should you perform the applied brake test?
• Only when parked
• At high speeds
• During the pre-trip inspection before moving
• After braking in traffic

This test ensures that brakes apply properly before the vehicle moves.

• How do you check the slack adjuster on a S-cam brake?
• Measure tire tread
• Listen for air leaks
• Pull it by hand with brakes released; it should move less than 1

inch

• Check fluid level
• / 4