GM Service Manual Online
For 1990-2009 cars only

If your vehicle has all-wheel drive (AWD), the AWD system operates automatically without any action required by the driver. If the front drive wheels begin to slip, the rear wheels will automatically begin to drive the vehicle as required. There may be a slight engagement noise during hard use but this is normal.

During heavy AWD applications, the engine torque may be reduced to protect AWD system components. If the vehicle is exposed to extended heavy AWD usage, the AWD system will shut itself off to protect the system from overheating. When the system cools down, the AWD system will activate itself again automatically; this cool-down can take up to 20 minutes depending on outside temperature and vehicle use.