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 Engine Control Module (ECM) received a message from the OEM VECU via the J1939 data link, indicating the remote throttle signal wire or enable switch was shorted high or shorted low.

Action Taken When the Fault Code is ActiveThe ECM illuminates the red STOP ENGINE lamp immediately after 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 ECM will turn off the red STOP ENGINE lamp immediately after the diagnostic runs and passes.For On-Board Diagnostics (OBD) engines, the ECM will extinguish the Malfunction Indicator Lamp (MIL) after three consecutive trips where 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 TalkThis fault can occur when the OEM VECU detects an error on the remote throttle and or remote throttle enable switch. The ECM has been set up properly (components enabled and OEM VECU source addressed correctly) to receive multiplexed information for the remote throttle enable switch states and remote accelerator position over the J1939 data link from an OEM VECU, and the OEM VECU is transmitting the message for that component. Most OEM VECUs will not have the circuitry to detect a remote throttle switch error.

The two types of errors that can occur for this fault are:

The OEM VECU determines that the remote throttle signal line is shorted high or shorted low. This fault status is transmitted to the Cummins® ECM on the J1939 data link, which causes this fault to occur in the Cummins® ECM.When the remote throttle enable switch has a shorted high or shorted low error detected by the OEM VECU, this fault status is transmitted to the ECM on the J1939 data link, which causes this fault to occur in the ECM. Most OEM VECUs will not incorporate fault detection on a switch.NOTE: It is still possible to get a Fault Code 285 or 286, if there is an incorrect setup in the OEM VECU or Cummins® ECM for other components, or the remote throttle and remote throttle switch, or the data link is damaged. The OEM configurations must multiplex the remote throttle and remote throttle switch inputs together to allow the use of the J1939 multiplexing feature for these components. The INSITE™ electronic service tool can be used to monitor multiplexed components.

Reference the appropriate OEM wiring diagram when troubleshooting circuits that utilize wiring supplied by the OEM.

Possible Cause:1) OEM issue2) ECM calibration