What is the procedure to test the trailer service brakes?

The procedure to test the trailer service brakes involves releasing the parking brakes and then applying the trailer hand brake while the vehicle is in motion. This method allows you to check whether the brakes are functioning effectively and respond adequately under load, as it simulates real driving conditions. By applying the brake while moving, you can observe the trailer’s reaction and ensure that it properly adheres and slows the trailer down, which is vital for safe operation.

The other options do not effectively test the trailer service brakes: moving forward slowly and applying the parking brake does not isolate the service brakes for effective testing; applying brakes while stationary does not provide real-time performance feedback; and only applying brakes while uphill does not allow for a comprehensive assessment, as brakes need to be tested in various conditions to ensure their reliability.