Louisiana CDL Air Brake Test (LA) 2026

4.9 out of 5 (54 votes)
80% Passing score
20 Questions
4 Mistakes allowed
Preparing for your commercial driver's license in Louisiana requires thorough knowledge and understanding of air brake systems. Our Louisiana air brakes CDL test provides an excellent opportunity for you to master the essentials needed for safe driving and to earn your air brakes endorsement. This DMV practice test features 20 multiple-choice questions designed to comprehensively cover all aspects of air brake systems, including compressors, reservoirs, and brake chambers. The Louisiana practice driving test focuses on both theoretical knowledge and practical applications of air brake systems, emphasizing the operational principles and safety protocols vital for every driver. It also delves into the specifics of brake lag time, a crucial factor in air brakes that affects stopping distances. With questions tailored to Louisiana's specific driving laws and regulations, you're not just preparing for a test; you're preparing to drive safely and legally across the state. Our Louisiana permit practice test is equipped with a variety of study aids to enhance your learning experience. If you encounter a challenging question, hints are available to nudge you toward the right answer. Should you answer incorrectly, the test immediately provides detailed explanations, clarifying the correct response and expanding your understanding of the topic. Additionally, for visual learners, many of the questions are supported by images and diagrams that help clarify complex concepts. These visual aids ensure that you not only remember the information but also understand it thoroughly. To pass the Louisiana DMV air brake test, you need to correctly answer at least 16 out of the 20 questions. Achieving this score confirms that you have a solid grasp of the fundamental concepts necessary for operating vehicles with air brakes effectively. This test serves as both a learning tool and a measure of your readiness for the air brakes endorsement, setting you on the path to becoming a proficient commercial vehicle driver in Louisiana.
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Sample Louisiana Air Brakes Test Questions

Question 1

During an air-compressor governor check, pumping should normally stop at about what pressure?

  1. A 80 psi
  2. B 100 psi
  3. C 125 psi
  4. D 150 psi

Correct answer: C – 125 psi

Louisiana's air-brake inspection procedure states that the compressor should normally stop pumping at about 125 psi. This is the governor's cut-out pressure. Because vehicle specifications can vary, the driver must also know and follow the manufacturer's specified pressure for the vehicle being inspected.

Source: Louisiana Commercial Driver License Manual — § 5.3.3, “Check Air Compressor Governor Cut-in and Cut-out Pressures”

Question 2

Which condition can cause air brakes to fade or fail?

  1. A Operating during heavy rain
  2. B Excessive use of the service brakes
  3. C Driving in congested traffic
  4. D Applying the parking brake after stopping

Correct answer: B – Excessive use of the service brakes

Excessive use of the service brakes causes overheating and can lead to brake fade. Heat reduces friction in the brake linings and can expand the drums, reducing braking force. On a long downgrade, the vehicle should be placed in the proper low gear so engine braking performs most of the speed-control work.

Source: Louisiana Commercial Driver License Manual — § 5.4.5, “Brake Fading or Failure”

Question 3

How should you normally brake a tractor-trailer combination equipped with ABS?

  1. A Use normal braking procedures
  2. B Brake harder than usual during every stop
  3. C Immediately slam on the brakes whenever slowing
  4. D Use stab braking as the standard method

Correct answer: A – Use normal braking procedures

Use normal braking procedures and apply only the force necessary to stop safely while maintaining control. As the combination slows, monitor both the tractor and trailer. If either begins moving out of line, reduce brake pressure when it is safe to do so until control is regained.

Source: Louisiana Commercial Driver License Manual — § 5.4.2, “Braking with ABS”

Question 4

During an applied air-leakage test on a combination vehicle, a loss of 1 psi in one minute is the maximum permitted pressure drop.

  1. A TRUE
  2. B FALSE

Correct answer: B – FALSE

False. Under Louisiana's inspection procedure, with the engine off and the foot brake fully applied, a combination vehicle may not lose more than 4 psi in one minute. A pressure drop greater than that indicates excessive leakage that must be found and repaired before the vehicle is driven.

Source: Louisiana Commercial Driver License Manual — § 5.3.3, “Test Air Leakage Rate”, 49 CFR § 570.57(a)(5) — Air brake system and air-over-hydraulic brake subsystem

Question 5

During an air-compressor governor check, pumping should normally begin again at about what pressure?

  1. A 80 psi
  2. B 100 psi
  3. C 125 psi
  4. D 150 psi

Correct answer: B – 100 psi

The air compressor should normally begin pumping again at about 100 psi. This is called the governor cut-in pressure. During the check, reduce tank pressure by applying and releasing the brake, then verify that the gauge begins rising at approximately the manufacturer's specified cut-in pressure.

Source: Louisiana Commercial Driver License Manual — § 5.3.3, “Check Air Compressor Governor Cut-in and Cut-out Pressures”

Question 6

What is the purpose of the separate air supply used with dual parking control valves?

  1. A To balance service-brake pressure while driving
  2. B To keep the vehicle parked without applying spring brakes
  3. C To increase service-brake pressure when the main supply is low
  4. D To temporarily release the spring brakes so the vehicle can be moved in an emergency

Correct answer: D – To temporarily release the spring brakes so the vehicle can be moved in an emergency

Some vehicles have a separate air tank that can temporarily release the spring brakes after main air pressure is lost. This allows the vehicle to be moved during an emergency. The separate supply can release the brakes only a few times, so the movement must be carefully planned to avoid exhausting the available air.

Source: Louisiana Commercial Driver License Manual — § 5.1, “Dual Parking Control Valves”

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