Air Brakes
This endorsement is required for driving a vehicle with air brakes. To receive this endorsement, applicants must pass a written test. The test consists of 25 multiple choice questions. Each question has four answer choices. To pass, the applicant must answer at least 20 questions correctly. Test questions come from the Commercial Driver License Manual. Questions come from the chapter covering: Air Brakes. The Air Brakes endorsement may be used with the Class A, B or C CDL.
Number of Question
Passing Score
13. If using air tanks with manually operated drains, how often should you drain the tanks?
Explanation
In an air brake system with manually operated drains, the tanks should be drained at the end of each day of driving.
14. When starting a vehicle with dual air brakes, pressure of ____ should be built up in the system before it is driven.
Explanation
Before driving a vehicle with a dual air brake system, allow time for the air compressor to build up pressure of at least 100 psi in both the primary and secondary systems.
15. Do not use the parking brake when parking if:
Explanation
A parking brake should not be used if the vehicle's brakes are very hot from use on a steep downgrade or if the brakes are very wet and temperatures are freezing. Using the parking brake when brakes are hot could cause damage to the brakes, and using the brakes when they are wet in freezing weather may cause the brakes to ice up, rendering the vehicle immobile.
16. If the low pressure warning light comes on while you are driving:
Explanation
When driving a vehicle with air brakes, if the low air pressure warning light comes on, it is important for you to stop and safely park your vehicle as soon as possible. There may be a leak in the system. Controlled braking will remain possible only as long as there is enough air left in the tanks.
17. When operating a vehicle with a dual brake system, a driver should:
Explanation
Before driving a vehicle with a dual air system, allow time for the air compressor to build up a minimum pressure of 100 psi in both the primary and secondary systems.
18. The safety valve located on the first tank opens:
Explanation
In an air brake system, the first tank that receives compressed air has a safety valve that releases air if the pressure gets too high. It is usually set to open at 150 psi. If the valve must open, there is a fault in the system that should be repaired by a mechanic.
See the exact questions that will be on the 2026 Massachusetts DMV exam.
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