GMC 2006 Sierra - Manual (Page 517)

Secondary Latch System
Your vehicle has an underbody-mounted tire hoist
assembly equipped with a secondary latch system. It is
designed to stop the spare tire from suddenly falling
off your vehicle. For the secondary latch to work,
the spare must be installed with the valve stem pointing
down. See Storing a Flat or Spare Tire and Tools on
page 5-108.
{ 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.
To release the spare tire from the secondary latch,
do the following:
1. Check under the vehicle to see if the cable end
is visible.
If the cable is not visible, proceed to Step 6.
2. If it is visible, first try to tighten the cable by turning
the wheel wrench clockwise until you hear two
clicks or feel it skip twice. You cannot overtighten
the cable.
3. Loosen the cable by turning the wheel wrench
counterclockwise three or four turns.
5-105