GMC 2002 Envoy Owner's Manual page 58

With this system, use the LATCH system instead of the
vehicle's safety belts to secure a child restraint.
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CAUTION:
-
If a LATCH type child restraint isn't attached to
its anchorage points, the restraint won't be able
to protect a child sitting there. In a crash, the
child could be seriously injured or killed. Make
-
sure that a LATCH type child restraint is
properly installed using the anchorage points, or
use the vehicle's safety belts to secure the
restraint. See "Securing a Child Restraint in a
Rear Outside Seat Position" in the Index for
information on how to secure a child restraint in
your vehicle using the vehicle's safety belts.