Theory Of Operation
WARNING: This page is about a different car, the 2005 Jeep Grand Cherokee. However, it is still accessible from the selected car via links, so may be relevant.
Some NGC controllers communicate with other controllers over the CAN C bus. The transmission controller 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, therefor if the Engine Controller is unable to communicate with the Transmission Controller, the Engine Controller will light the MIL.