To test the air service brakes you should:

• A. Brake firmly while slowly moving forward.
• B. Blow the horn while applying brakes.
• C. Turn off the engine and coast.
• D. Do a sharp stop from high speed.

Answer: (A)

Testing air service brakes means checking how the brakes respond under normal driving conditions, but at a safe, low speed. Brake firmly while moving slowly to ensure the brakes engage quickly and evenly, stop in a straight line, and don’t drag or pull to one side. This simulates a real stop and confirms the system’s effectiveness before you rely on it at higher speeds. The other options don’t assess brake performance: blowing the horn while braking doesn’t test braking action; turning off the engine would reduce or cut off the air supply and is unsafe; and stopping sharply from high speed is dangerous and not how brakes are evaluated in a typical test.