Theory Of Operation
WARNING: This page is about a different car, the 2012 Jeep Patriot and 2012 Jeep Compass. However, it is still accessible from the selected car via links, so may be relevant.
The Transmission Range Sensor (TRS) has a contact point for each shift lever position. The Transmission Control Module (TCM) monitors the signal from the TRS which specifies the shift lever position. The TCM also broadcast the shift lever position over the CAN BUS to other modules.