Q: It is called versatrak
A: On the rendezvous the AWD system is always active - there is no swtich for the driver to deal with. How it works - The rendezvous is a FWD vehicle with a rear drive module (RDM - similar to a rear axle) that powers the rear wheels when front wheel slippage is detected. A clutch in the RDM is activated either electrically through the ABS system or mechanically with a hydraulic pump between the drivehaft and the RDM to temporarily power the rear wheels. The rendezvous has an older design (likely mechanical) AWD - newer systems can vary the torque split front to back and send more power rearward in times of high acceleration, etc.