To test the trailer service brakes, what should you do when at normal air pressure?

To test the trailer service brakes effectively, it's important to first ensure that you are at normal air pressure. Releasing the parking brakes and moving the vehicle forward slowly allows for a proper assessment of the brakes' functionality. As the vehicle moves, the trailer's service brakes engage with the applied pressure, enabling you to observe how well they respond. If the brakes are functioning correctly, you should feel a consistent response when you apply the brake pedal.

This method reflects real-world conditions in which the brakes would normally operate, providing a practical evaluation of their functionality. Conducting the test while in motion is critical since stationary tests might not provide the same feedback as actual movement would. The other methods, such as engaging the parking brakes while moving or testing the brakes when the vehicle is stationary, do not provide the same insight into the braking system's operation under load or performance when the vehicle is in motion.