This is from my 2006 sv6 owners manual, hope it helps.
ALL WHEEL DRIVE DISABLED
If your vehicle has the all-wheel drive system, this message will display when there is a spare tire on the vehicle, or when the anti-lock brake system warning light comes on, or when the rear differential fluid is overheating. This message will turn off when the differential fluid cools.
The all-wheel drive system will be disabled until the compact spare tire is replaced by a full-size tire. If the warning message is still on after putting on the full-size tire, you need to reset the warning message.
To reset the warning message, turn the ignition off and then back on again. If the message stays on, see your GM dealer right away. See All-Wheel Drive
(AWD) System on page 4-12 for more information.