What should you do after shutting off the trailer air supply and locking the trailer brakes?

After shutting off the trailer air supply and locking the trailer brakes, the correct action is to back up gently. This process is crucial because it helps to ensure that the trailer is properly secured to the tractor. When you back up, it allows the fifth wheel to settle into place and engage with the kingpin on the trailer. This ensures that the connection is secure before you proceed with any further actions, like disconnecting the tractor.

Backing up gently serves as a safety measure to check the engagement of the trailer and tractor. If the connection is not secure, there could be serious safety risks when attempting to move the combination vehicle afterward. Additionally, doing this before disconnecting the tractor provides a final check that the trailer is locked in position and that the tractor will not move unexpectedly.

Engaging the trailer in this way prepares the setup for safe operation and eliminates the risk of disconnection while in transit. Therefore, this action is a fundamental part of the process whenever handling combination vehicles.