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    ON Air Brake Test 4 2025

    Based on the 2025 ON CDL manual
    Questions: 50
    Mistakes allowed: 10
    Passing score: 80%
    Ensuring the accuracy and quality of our practice tests is paramount. Learn more about our rigorous standards in our Commitment to Accuracy article.
    What to expect on the official exam
    How many questions:25
    How many correct answers to pass:20
    Passing score:80%

    Do you want to drive a truck in Ontario? To be a commercial driver in this province, you need a licence that is specific to the type of truck you want to drive. As a truck driver, you are a critical part of the transportation industry. The power and size of large trucks are awe-inspiring. Even while you’re driving safely, the smallest mistake can cause serious damage. Before you can get your commercial driver’s licence, you must pass both a written and practical test. The written test (also known as the Ontario commercial driver’s licence knowledge exam) has several multiple-choice questions. You must get at least an 80% to pass the knowledge examination. This 50-question practice test will help you to prepare for the Ontario (ON) Air Brake written test required to get your commercial driver’s licence. As you answer the questions on this test, we recommend checking each question’s explanation to gain further insight into the rule behind it. All questions on this test are based on the 2025 ON commercial driver’s guide. Good luck and drive safely!

    4.67 out of 5 • 3 votes.
    Based on 2025 ON commercial driver's license manual
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    List of questions (classic view)
    1. How often should the air tanks be drained?
    2. On a tractor-trailer, if the supply and service lines to the trailer are cross-connected, what may happen?
    3. How do you release DD3 safety actuator brakes?
    4. When you're going to tow a trailer, how can you tell if the trailer's antilock braking system (ABS) is working?
    5. Wedge brakes are
    6. The purpose of the tractor protection valve is
    7. To test the tractor protection valve, disconnect the trailer service line and
    8. In a tractor-trailer, the connections between the tractor and the trailer include which of the following components?
    9. The hand valve control ("spike") applies
    10. Which brakes are more powerful, the spring brakes or the service brakes?
    11. Which of the following is NOT a part of a truck's braking system?
    12. A tractor-trailer's braking system supplies compressed air to which trailer brakes FIRST?
    13. An S-cam is found in
    14. When coupling a tractor to a trailer, how many air lines do you have to connect?
    15. If there is a loss of air to the service brakes in a trailer with a spring brake priority system, how can you brake the trailer to a stop?
    16. In a trailer with a spring brake priority system, compressed air is supplied to which brakes FIRST?
    17. How many air lines must be connected to a DD3 safety actuator brake chamber?
    18. The tractor protection valve closes to stop the flow of compressed air to
    19. To uncouple your tractor from the trailer, how should you set the trailer air supply valve?
    20. Which of the following is not a component of a wedge brake?
    21. How often should you check brake chamber pushrod travel?
    22. Which of the following is a part of a disc brake?
    23. In an air braking system, which of the following is not commonly part of a disc brake?
    24. Which of the following are helpful in reducing heat in the air brake system?
    25. Which of the following can affect pushrod stroke?
    26. If you find a major defect in the air brake system, you should
    27. How can you determine applied pushrod stroke?
    28. Which is least likely to cause brake drums to overheat?
    29. When must full braking capability be available?
    30. Assuming good traction and constant vehicle weight, if you double your vehicle's speed, your vehicle's braking distance will be
    31. In an air brake system, what does a governor do?
    32. Which of the following is the best way to inspect an air compressor?
    33. When can you adjust automatic slack adjusters?
    34. If the outer layer of an air line is damaged, but the inner tube is still OK, what should you do?
    35. To make sure the air tanks are securely attached to your vehicle, you should
    36. Before inspecting your air brakes, you should
    37. Your vehicle passes the tug test of the parking brakes if
    38. If the brake chambers on opposite sides of an axle are of different sizes, the result may be
    39. To check the brake chambers for leaks, you should
    40. in a drum brake, the brake lining is fastened to
    41. What occurs when the brake drums undergo excessive heating?
    42. Normal air brake tank pressures are
    43. What letter is added to your licence when you apply for an Air Brake Endorsement?
    44. What mechanism drives the air compressor?
    45. What should you do if your brakes overheat due to continual use or improper adjustment?
    46. What term refers to the pressure level at which the air compressor stops pumping air?
    47. The pressure range of the normal air brake system is dictated by the points at which the air compressor ...
    48. Cut-in pressure should never be less than
    49. Can brake fluid compress similarly to air in air brake systems?
    50. What role does the air compressor play?

    ON Air Brake Test 4

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    Do you want to drive a truck in Ontario? To be a commercial driver in this province, you need a licence that is specific to the type of truck you want to drive. As a truck driver, you are a critical part of the transportation industry. The power and size of large trucks are awe-inspiring. Even while you’re driving safely, the smallest mistake can cause serious damage. Before you can get your commercial driver’s licence, you must pass both a written and practical test. The written test (also known as the Ontario commercial driver’s licence knowledge exam) has several multiple-choice questions. You must get at least an 80% to pass the knowledge examination. This 50-question practice test will help you to prepare for the Ontario (ON) Air Brake written test required to get your commercial driver’s licence. As you answer the questions on this test, we recommend checking each question’s explanation to gain further insight into the rule behind it. All questions on this test are based on the 2025 ON commercial driver’s guide. Good luck and drive safely!

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