Theory Of Operation
WARNING: This page is about a different car, the 2009 Jeep Liberty. However, it is still accessible from the selected car via links, so may be relevant.
The Final Control Module (FDCM) communicates with other controllers over the CAN C bus. The FDCM continuously monitors the bus activity and receives the messages it needs. The CAN C bus is also used to communicate FDCM MIL status to the Engine Controller, therefor if the Engine Controller is unable to communicate with the FDCM, the Engine Controller will light the MIL.