GMC Yukon XL Denali 2005 Owner's Manual page 75

5. Pull the rest of the shoulder belt all the way out of 6. To tighten the belt, push down on the child restraint,
the retractor to set the lock. 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 from the retractor once the lock has
been set.
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