Theory Of Operation
WARNING: This page is about a different car, the 2013 RAM 1500. However, it is still accessible from the selected car via links, so may be relevant.
The vehicle control modules communicate over the CAN C BUS. The Transmission Control Module (TCM) continuously monitors BUS activity. The CAN C BUS is used to communicate transmission MIL status to the PCM. If the PCM is unable to communicate with the TCM, a DTC sets and the PCM will illuminate the MIL.