Transmission Control Module (TCM)
WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.
The TCM monitors the data from the ABS controller and RDM for proper operating conditions. If inappropriate conditions are present, the TCM commands the differential clutch pump actuator check valve closed, disabling the AWD system. The TCM also commands the AWD disable indicator on.