GMC 2007 Sierra 1500 Pickup Owner's Manual page 77

6. To tighten the belt, push down on the child
restraint, pull the shoulder portion of the belt
to tighten the lap portion of the belt and
feed the shoulder belt back into the retractor.
If you are using a forward-facing child
restraint, you may find it helpful to use your
knee to push down on the child restraint
as you tighten the belt. You should not be able
to pull more of the belt out of the retractor
once the lock has been set.
7. Push and pull the child restraint in different
directions to be sure it is secure.
To remove the child restraint, just unbuckle the
vehicle's safety belt and let it go back all the way.
The safety belt will move freely again and be
ready to work for an adult or larger child
passenger.
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