Cadillac 2009 DTS Owner's Manual page 58

5. Pull the rest of the shoulder belt all the way out of
the retractor to set the lock.
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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. 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.
7. Push and pull the child restraint in different
directions to be sure it is secure.
If the airbags are off, the off indicator in the passenger
airbag status indicator will come on and stay on
when the vehicle is started.