Cadillac 2010 STS - Manual (Page 77)

4. Pull the rest of the shoulder belt all the way out of
the retractor to set the lock.
5. 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. When
installing a forward-facing child restraint, it may be
helpful to use your knee to push down on the child
restraint as you tighten the belt.
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