GMC 2004 Envoy Owner's Manual page 386

Secondary Latch System
Your vehicle has an underbody mounted tire hoist
assembly equipped with a secondary latch system.
It's designed to stop the spare or flat road tire
from suddenly falling off your vehicle if the cable holding
the spare tire is damaged. For the secondary latch to
work, the spare tire must be stored with the valve stem
pointing up. See "Storing a Flat or Spare Tire and
Tools" for instructions on storing the spare tire correctly.
CAUTION:
{
Before beginning this procedure read all the
instructions. Failure to read and follow the
instructions could damage the hoist assembly
and you and others could get hurt. Read and
follow the instructions listed below.
5-78
CAUTION:
{
Someone standing too close during the
procedure could be injured by the jack. If the
spare tire does not slide off the jack completely,
make sure no one is behind you or on either
side of you as you pull the jack out from the
spare.
To release the spare tire from the secondary latch do
the following:
1. Check under the
vehicle to see if the
cable is visible.