What is the procedure to check the kingpin connection after locking it into the fifth wheel?

Performing a tug test is essential to ensure that the kingpin is securely locked into the fifth wheel. This test involves gently pulling forward with the tractor to verify that the connection is properly secured. If the kingpin is not locked in place, the trailer could detach while in motion, leading to dangerous situations on the road.

This procedure is crucial because visual inspections alone may not always reveal a poor connection, and other methods, such as checking trailer lights or attempting to move the trailer by hand, do not reliably assess the security of the coupling. The tug test specifically checks the functional engagement of the kingpin with the fifth wheel, making it a necessary step in the pre-trip inspection process for combination vehicles.