GMC 2008 Acadia - Manual (Page 395)

Secondary Latch System
Your vehicle has an underbody mounted tire hoist
assembly that has a secondary latch system. It is
designed to stop the compact spare tire from suddenly
falling off your vehicle if the cable holding the spare
tire is damaged. For the secondary latch to work, the tire
must be stowed with the valve stem pointing down.
See Storing a Flat or Spare Tire and Tools on page 5-84
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 next.
To release the spare tire from the secondary latch:
{ 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 under spare.
1. If the cable is not visible, start this procedure at
Step 3.
5-81