ON Air Brake Test 4

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!

Unlock full access with Premium

Perfect for first-time and renewal commercial applicants, and those adding endorsements
Triple-checked for accuracy

This test is a Premium member exclusive. You'll get

All 1,500+ exam-like questions specific to Ontario

Interactive learning with AI personal tutor

Get your money back if you don’t pass

What you need to know

4.67 out of 5 • 3 votes

Verified by Steven Litvintchouk, M.S., Chief Educational Researcher, Member of ACES. See our detailed commitment to accuracy and quality in our practice tests.

What to expect on the official exam

questions

correct answers to pass

passing score

Our commitment to accuracy and quality in our practice tests

Explore our rigorous, multi-tiered verification process that ensures each question mirrors the official manual for unparalleled accuracy.

Written by Andrei Zakhareuski Updated over a week ago

At Tests.ca, we understand the importance of reliable and accurate practice tests to help you prepare for your driver's knowledge exam. That's why we've developed a meticulous process to create and continually update our practice questions, ensuring they reflect the most current driving laws and regulations.

Here's an inside look at how we maintain the highest quality in our practice tests.

Content Creation and Verification Process

Alignment with Official Driving Handbooks:
Every question we develop is based on the most recent version of each province's official driving manual. Our team regularly monitors each province's official website for the latest updates to ensure our practice tests are always aligned with the most current information.
Community Feedback Integration:
We leverage feedback from our vast community of users to understand which topics are most frequently tested. This helps us focus on the areas that are most relevant and beneficial for your preparation.
Expert Content Creation:
Our in-house editor, Steven, who has extensive experience in driver education, crafts each question with precision. He conducts a thorough review of each question against the official manuals to ensure accuracy.
Rigorous Review Process:
Once Steven has finalized a set of questions, our team conducts a joint review session. This second level of scrutiny involves content accuracy, proofreading, and fact-checking to eliminate any errors.
User Feedback Mechanism:
After a question goes live on our site, we keep the lines of communication open. Each question features a feedback button, inviting users to report any issues or errors. This continuous feedback loop allows us to address and rectify any concerns promptly.
Responsive Updates:
In line with our commitment to accuracy, we quickly update our practice questions to reflect any changes in the provincial government manuals. Additionally, we update the free electronic copy of the state's driver's license manuals on our site, typically within a few days after the government publishes them.

Our thorough quality control process ensures that you have access to practice tests that are as accurate and up-to-date as possible. We believe in the power of well-prepared drivers and are dedicated to providing you with the best study tools to help you succeed on your driver's knowledge exam.

More resources

Are you in another province?

List of questions (classic view)

How often should the air tanks be drained?
On a tractor-trailer, if the supply and service lines to the trailer are cross-connected, what may happen?
How do you release DD3 safety actuator brakes?
When you're going to tow a trailer, how can you tell if the trailer's antilock braking system (ABS) is working?
Wedge brakes are
The purpose of the tractor protection valve is
To test the tractor protection valve, disconnect the trailer service line and
In a tractor-trailer, the connections between the tractor and the trailer include which of the following components?
The hand valve control ("spike") applies
Which brakes are more powerful, the spring brakes or the service brakes?
Which of the following is NOT a part of a truck's braking system?
A tractor-trailer's braking system supplies compressed air to which trailer brakes FIRST?
An S-cam is found in
When coupling a tractor to a trailer, how many air lines do you have to connect?
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?
In a trailer with a spring brake priority system, compressed air is supplied to which brakes FIRST?
How many air lines must be connected to a DD3 safety actuator brake chamber?
The tractor protection valve closes to stop the flow of compressed air to
To uncouple your tractor from the trailer, how should you set the trailer air supply valve?
Which of the following is not a component of a wedge brake?
How often should you check brake chamber pushrod travel?
Which of the following is a part of a disc brake?
In an air braking system, which of the following is not commonly part of a disc brake?
Which of the following are helpful in reducing heat in the air brake system?
Which of the following can affect pushrod stroke?
If you find a major defect in the air brake system, you should
How can you determine applied pushrod stroke?
Which is least likely to cause brake drums to overheat?
When must full braking capability be available?
Assuming good traction and constant vehicle weight, if you double your vehicle's speed, your vehicle's braking distance will be
In an air brake system, what does a governor do?
Which of the following is the best way to inspect an air compressor?
When can you adjust automatic slack adjusters?
If the outer layer of an air line is damaged, but the inner tube is still OK, what should you do?
To make sure the air tanks are securely attached to your vehicle, you should
Before inspecting your air brakes, you should
Your vehicle passes the tug test of the parking brakes if
If the brake chambers on opposite sides of an axle are of different sizes, the result may be
To check the brake chambers for leaks, you should
in a drum brake, the brake lining is fastened to
What occurs when the brake drums undergo excessive heating?
Normal air brake tank pressures are
What letter is added to your licence when you apply for an Air Brake Endorsement?
What mechanism drives the air compressor?
What should you do if your brakes overheat due to continual use or improper adjustment?
What term refers to the pressure level at which the air compressor stops pumping air?
The pressure range of the normal air brake system is dictated by the points at which the air compressor ...
Cut-in pressure should never be less than
Can brake fluid compress similarly to air in air brake systems?
What role does the air compressor play?