Air Brakes Practice Test
The Air Brakes endorsement is required for any CDL driver operating a vehicle equipped with air brakes. Our free practice test covers system components, inspection procedures, and safe operation so you can pass the knowledge exam with confidence.
What's on the Air Brakes Test
The air brakes knowledge test covers the components and operation of air brake systems, including how to inspect them, identify defects, and operate safely. You'll be tested on system parts, pressure readings, stopping procedures, and emergency situations.
Who Needs an Air Brakes Endorsement
You need an Air Brakes endorsement if you plan to drive any commercial vehicle equipped with air brakes, which includes most Class A tractors and many Class B trucks and buses. Without the endorsement, your CDL will carry an 'L' restriction that prohibits you from operating air brake vehicles. If you take your skills test in a vehicle without air brakes, you'll also receive the restriction.
Sample Practice Questions
1. At what pressure should the low air pressure warning signal activate?
- A.40 psi
- B.60 psi
- C.80 psi
- D.100 psi
Answer: B. The low pressure warning signal must activate before the air tank pressure drops below 60 psi to give the driver time to stop safely.
2. What are the three braking systems on an air brake vehicle?
- A.Front, rear, and trailer
- B.Service, parking, and emergency
- C.Primary, secondary, and reserve
- D.Foot, hand, and engine
Answer: B. The three systems are service brakes (for normal stopping), parking brakes (for holding), and emergency brakes (for stopping during a system failure).
3. How often should you drain the air tanks?
- A.Weekly
- B.Monthly
- C.After each working day
- D.Only when full
Answer: C. Moisture and oil can build up in the air tanks and cause brake failure, so you should drain them at the end of each working day.
4. What is the purpose of the alcohol evaporator in an air brake system?
- A.To cool the air compressor
- B.To prevent ice in the air lines in cold weather
- C.To lubricate the brake drums
- D.To reduce air pressure
Answer: B. The alcohol evaporator adds alcohol to the air system to stop ice from forming in the air lines during freezing weather.
5. What does the air compressor governor control?
- A.Brake pressure only
- B.When the compressor pumps air into the tanks
- C.The speed of the vehicle
- D.The parking brake
Answer: B. The governor controls when the compressor pumps air into the storage tanks, cutting out when pressure reaches around 125 psi and cutting back in at about 100 psi.
Frequently Asked Questions
How many questions are on the Air Brakes endorsement test?
The air brakes knowledge test typically has 25 questions. You must answer at least 20 correctly (80%) to pass.
What happens if I don't get the Air Brakes endorsement?
Your CDL will carry an 'L' (air brake) restriction, meaning you cannot legally drive any vehicle equipped with air brakes.
Can I remove the air brake restriction later?
Yes. You can take the air brakes knowledge test and skills test in an air brake-equipped vehicle to have the restriction removed.
Is the air brakes test hard?
It can be challenging if you're not familiar with air brake system components. Our free practice test helps you learn the parts and procedures so you can pass on your first try.
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