Alabama CDL Air Brake Test (AL) 2026

5 out of 5 (54 votes)
80% Passing score
20 Questions
4 Mistakes allowed
Welcome to the ultimate Alabama CDL air brakes practice test designed specifically for aspiring commercial drivers in our great state. This comprehensive Alabama CDL air brake practice test features 20 multiple-choice questions that thoroughly cover the critical aspects of air brake systems. As you work through the test, you will gain in-depth knowledge of key components such as compressors, reservoirs, and brake chambers, along with an understanding of the operational principles and safety protocols essential for air brake systems. One unique aspect of the Alabama CDL air brakes practice test is its focus on the brake lag time specific to air brakes. This crucial factor must be considered when calculating stopping distances, ensuring that you are well-prepared for real-world driving situations. With no time limits, you can take as much time as you need to carefully consider each question, allowing you to fully understand and retain the information presented. To further enhance your learning experience, the Alabama CDL air brakes practice test provides immediate feedback on each question. Detailed explanations are included, helping you to understand why a particular answer is correct or incorrect. This approach not only aids in reinforcing your knowledge but also ensures that you grasp the underlying concepts necessary for mastering air brake operation. Accessibility is another key feature of this Alabama DMV air brake test. Whether you prefer to study on your mobile device, desktop, or through a mobile app, you can easily access the test anytime, anywhere. This flexibility allows you to fit your study sessions into your busy schedule, making it convenient to prepare for your CDL air brake endorsement. By correctly answering at least 16 out of the 20 questions, you will achieve a passing score, demonstrating your readiness for the commercial driver's license air brakes endorsement. This Alabama CDL air brake practice test is designed to ensure that you have a solid foundation in air brake systems, preparing you for safe and effective driving.
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Sample Alabama Air Brakes Test Questions

Question 1

On a tractor, truck, or bus, which indicator shows that the vehicle is equipped with ABS?

  1. A A red ABS lamp on the instrument panel
  2. B A yellow ABS malfunction lamp on the instrument panel
  3. C A red ABS lamp on the vehicle's left side
  4. D A red ABS lamp on the vehicle's right side

Correct answer: B – A yellow ABS malfunction lamp on the instrument panel

The Alabama CDL manual identifies a yellow ABS malfunction lamp on the instrument panel of tractors, trucks, and buses. Trailers generally have a yellow lamp on the left side near a front or rear corner. The lamp normally illuminates briefly during its start-up check and then goes out.

Source: Alabama Commercial Driver License Manual — § 5.1.16, “Antilock Braking Systems (ABS)”

Question 2

What function is performed by the air compressor governor?

  1. A It controls when the compressor pumps air into the storage tanks
  2. B It controls the braking pressure applied by the foot pedal
  3. C It determines whether the compressor needs repairs
  4. D It directly regulates the compressor's revolutions per minute

Correct answer: A – It controls when the compressor pumps air into the storage tanks

The governor controls the compressor's cut-in and cut-out operation. It stops the compressor from pumping when tank pressure reaches the cut-out level, generally around 125 psi in the manual's example. When pressure falls to the cut-in level, generally around 100 psi, the compressor begins pumping again.

Source: Alabama Commercial Driver License Manual — § 5.1.2, “Air Compressor Governor”

Question 3

Spring brakes apply automatically when air-system pressure becomes too low.

  1. A TRUE
  2. B FALSE

Correct answer: A – TRUE

During normal driving, air pressure holds the spring brakes off. If system pressure is lost, the springs apply the brakes mechanically. Tractor and straight-truck spring brakes commonly become fully applied between 20 and 45 psi, but the driver should stop safely before pressure becomes low enough for automatic application.

Source: Alabama Commercial Driver License Manual — § 5.1.14, “Spring Brakes”

Question 4

During the standard air-brake inspection check, the low-air warning device should activate before pressure drops below:

  1. A 40 psi
  2. B 50 psi
  3. C 55 psi
  4. D 90 psi

Correct answer: C – 55 psi

Alabama's current CDL inspection materials use 55 psi as the standard benchmark, while directing applicants to know the vehicle manufacturer's specification. Federal equipment rules require an air-pressure gauge and low-pressure warning system. For power units not subject to the applicable federal motor-vehicle safety standard, the warning must operate continuously at 55 psi and below, or one-half governor cut-out pressure, whichever is less.

Source: Alabama CDL Manual Supplement for Modernized Version — § 11M.1.2, “Air Brake or Hydraulic Brake Check”, 49 CFR § 393.51 – Warning Signals, Air Pressure and Vacuum Gauges

Question 5

If the ABS malfunctions, the vehicle's normal service brakes can still operate.

  1. A TRUE
  2. B FALSE

Correct answer: A – TRUE

An ABS malfunction does not normally eliminate the vehicle's regular service brakes. The vehicle can still brake, but the system may no longer help prevent wheel lockup during hard braking. Continue using normal braking technique and have the ABS serviced as soon as practical.

Source: Alabama Commercial Driver License Manual — § 2.18.7, “Braking If ABS Is Not Working”

Question 6

Brake fade can occur only in vehicles equipped with drum brakes.

  1. A TRUE
  2. B FALSE

Correct answer: B – FALSE

Brake fade is not limited to drum brakes. Excessive service-brake use creates heat that can reduce friction and braking effectiveness in drum or disc systems. Poorly adjusted brakes can worsen the problem because the remaining brakes must perform more work and may overheat sooner.

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

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