GMC 2000 Sonoma Owner's Manual page 229

This is the jack cover for the extended cab.
The cover for the regular cab is similar. To remove
it, turn the plastic wing nut counterclockwise.
Remove the jack cover.
Turn the wing nut counterclockwise and remove the
wheel blocks, jack and wheel wrench.
Your spare tire is stored underneath the rear of your
vehicle. See "Compact Spare Tire" later in this section
for more information about the compact spare.
5-20
NOTICE:
Never remove or store a tire from/to a storage
position under the vehicle while the vehicle is
supported by a jack. Always tighten the tire
fully against the underside of the vehicle when
storing it.
Be sure the chisel end of the wheel wrench connects into
the hoist shaft.
Insert the chisel end
of the wheel wrench, on
an angle, into the hole in
the rear bumper.