Theory of Operation
WARNING: This page is about a different car, the 2011 RAM Pickup. However, it is still accessible from the selected car via links, so may be relevant.
The Drive Train Control Module (DTCM) communicates with other controllers over the CAN C bus. The DTCM continuously monitors the bus activity and receives the messages it needs. The CAN C bus is also used to communicate DTCM MIL status to the Engine Controller, therefor if the Engine Controller is unable to communicate with the DTCM, the Engine Controller will light the MIL.