Lost Communications With the Engine Control Module (ECM)

Lost Communications With The Engine Control Module (ECM)

CIRCUIT DESCRIPTION
The engine control module (ECM), transmission control module (TCM) and electronic hydraulic control unit (EHCU) [ABS module] all communicate with the scan tool over the Class 2 serial data link. The EHCU receives transmission parameters necessary for correct ABS functions over the Class 2 link as well. However, the ECM and TCM communicate with each other over the controller area network (CAN) link. The CAN link is not used for communication with the scan tool and is shared only between the ECM and TCM (Except 12,000 lbs GVW) or between the ECM, TCM and glow plug controller (12,000 lbs GVW).

NOTE: If the battery supply voltage at the ECM (pin A-51) is lost, the ECM will still communicate with the scan tool and the engine will start and run normally. If ECM main relay voltage to the ECM is lost (must lose-voltage on all three ECM main relay power circuits), the scan tool will not communicate with the ECM.

Lost Communications With The Engine Control Module (ECM)
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls Connector End Views or Engine Control Module (ECM) Connector End Views

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