GMC 2004 Sierra 1500 Pickup Owner's Manual page 498

1500 Crew Cab
5-98
For regular cab models, the equipment you'll need is
behind the passenger's seat. For Extended and
crew cab models, the equipment is on the shelf behind
the passenger's side second row seat.
1. If there is a cover, move the seats forward and turn
the wing nut on the cover counterclockwise to
remove it. For crew cab models, pull up the second
row seat with the loop at the base of the seat
cushion to access the tools.
2. To release the bottle jack from its holder, turn the
knob on the bottle jack counterclockwise to lower
the jack head.
3. The wheel blocks and the wheel block retainer can
be removed by turning the wing nut
counterclockwise.
4. There is also a wing nut used to retain the storage
bag and tools. To remove it, turn the wing nut
counterclockwise.
You'll use the jack handle extensions and the wheel
wrench to remove the underbody-mounted spare tire.