CAN is an abbreviation for Controller Area Network.
The Engine Control Module (ECM) communicates with all databus capable control modules by a CAN Data Link.
The databus capable control modules (i.e. Engine Coolant Temperature sensor) are connected by two data bus wires which are twisted together (CAN_High and CAN_Low), and exchange information (messages) with the Engine Control Module (ECM). Missing information on the databus is then recognized and stored as a malfunction.
The Engine Control Module (ECM) illuminates the Malfunction Indicator Lamp (MIL) through the CAN data link and tells the Malfunction Indicator Lamp (MIL) to turn on, turn off, or blink.