Circuit DescriptionNormally, switches, accelerators, and other components are connected to the engine control module (ECM) directly through individual wires. Multiplexing allows those same components to be hard wired to an original equipment manufacturer (OEM) vehicle electronic control unit (VECU) or transmission electronic control unit (ECU) in the cab. Then component values and states from components such as sensors, accelerators, and switches can be transmitted from the OEM VECU to the Cummins® ECM over the SAE J1939 data link.

Messages sent from OEM VECUs or transmission ECUs are received by the Cummins® ECM and used for controlling the engine. The Cummins® ECM and OEM VECU(s) must be configured properly, so that proper operation of the multiplexed components will occur.

Component LocationThe SAE J1939 data link wiring and the SAE J1939 devices vary by OEM options.

Conditions for Running the DiagnosticsThis diagnostic runs continuously when the keyswitch is in the ON position or when the engine is running.

Conditions for Setting the Fault CodesThe ECM did not receive a message from the multiplexed device.

Action Taken When the Fault Code is ActiveThe ECM logs the fault code immediately when the diagnostic runs and fails.The multiplexed device will not operate.Conditions for Clearing the Fault CodeTo validate the repair, perform a key cycle, start the engine and let it idle for 1 minute.The fault code status displayed by INSITE™ electronic service tool will change to INACTIVE immediately after the diagnostic runs and passes.The Reset All Faults command in INSITE™ electronic service tool can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications.

Shop TalkPossible causes of this fault include:

Electrical problems with the SAE J1939 data link wiring such as grounded, shorted, or open circuitsThe ECM (or another SAE J1939 device) tying up communications by sending too many consecutive messagesThe external OEM controlling device has malfunctioned or can no longer transmit on the data link.Reference the appropriate OEM wiring diagram when troubleshooting circuits that utilize wiring supplied by the OEM.

For intermittent power supply and datalink communication issues with Aftertreatment Components, it is highly recommended that the OEM Power Distribution Center fuses and relays be thoroughly checked for loose, missing or intermittent connections.

Possible Cause:1) ECM calibration