Theory Of Operation
WARNING: This page is about a different car, the 2009 Dodge Sprinter. However, it is still accessible from the selected car via links, so may be relevant.
Some controllers communicate with other controllers over the CAN C bus. The Shift Lever Assembly (SLA) contains a Electronic Shift Module (ESM) that continuously monitors the bus activity and receives the messages it needs. The CAN C bus is also used to communicate transmission MIL status to the Engine Controller.