CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 285

SAE J1939 Multiplexing PGN Timeout Error – Abnormal Update Rate


Fault Code: 285
PID: S231
SPN: 639
FMI: 9/9
LAMP: Amber

SAE J1939 Multiplexing PGN Timeout Error – Abnormal Update Rate. The ECM expected information from a multiplexed device but did not receive it soon enough or did not receive it at all.

One or more multiplexed devices will not operate properly. One or more symptoms will occur.

ISX and ISM – SAE J1939 Multiplexing Circuit

Circuit Description

Normally, switches, accelerators and other components are connected to the engine electronic 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® engine ECM over the SAE J1939 Data link.

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

Component Location

The engine ECM is located on the intake side of the engine. Refer to Procedure 100-002 (Engine Diagrams) in Section E for a detailed component location view.

The J1939 data link wiring and VECU location varies by OEM. Refer to the OEM troubleshooting and repair manual.

Conditions for Running the Diagnostics

This diagnostic runs continuously when the keyswitch is in the ON position.

Conditions for Setting the Fault Codes

The ECM does not receive a valid J1939 message from a multiplexed device for more than 1 second.

The ECM detects an open or short circuit condition in the J1939 data link harness.

Action Taken When the Fault Code is Active

  • The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
  • The ECM will use a default state as an input for the multiplexed device.

Conditions for Clearing the Fault Code

The ECM will turn off the amber CHECK ENGINE light immediately after the diagnostic runs and passes.

Shop Talk

Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe™ Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM. Refer to Procedure 019-032 (ECM Calibration Code) in Section 19 in the corresponding Troubleshooting and Repair Manual for the engine being serviced.

When this fault code is active, some multiplexed devices may not function as desired.

This fault can occur for the following reasons:

  • When the ECM is set up properly (components enabled and OEM VECU source addressed correctly) to receive information from an OEM VECU, but the OEM VECU is actually transmitting a message that says that component is not available for multiplexing. This can be caused when a multiplexed component is enabled in the Cummins® ECM, but the OEM VECU source address of the VECU transmitting the component message is incorrect in the Cummins® ECM, or the OEM VECU is not set up to transmit the multiplexed component message.
  • This fault can also be caused by a malfunctioning J1939 data link connection between the OEM VECU and Cummins® ECM, a malfunctioning connection between the component and the OEM VECU, malfunctioning OEM VECU or malfunctioning Cummins® ECM. It may be necessary to contact the OEM for proper multiplexing configuration.

It is possible to use INSITE™ electronic service tool to monitor multiplexed components.

Refer to Troubleshooting Fault Code t05-285

Last Modified:  09-Jul-2010