You are uncoupling a trailer. After you shut off the trailer air supply and lock the trailer brakes, you should _________.

6.4.2 – Uncoupling Tractor-Semitrailers
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Step 2. Ease Pressure on Locking Jaws
Shut off trailer air supply to lock trailer brakes. Ease pressure on fifth wheel locking jaws by backing up gently. (This will help you release the fifth wheel locking lever.) Put parking brakes on while tractor is pushing against the kingpin. (This will hold rig with pressure off the locking jaws.)
[Commercial Driver's License Manual]