Cummins ISB CM850 (2003-06) Fault Code: 291 PID: SID 248 SPN: 625 FMI: 9 Proprietary Datalink Error (OEM/Vehicle Datalink) ? Abnormal Update Rate. The ECM cannot communicate with the immobilizer anti-theft system.

This fault can occur for the following reasons:

1)When the ECM is setup properly to receive information from an immobilizer anti-theft device, but the immobilizer anti-theft device may not actually be transmitting the message for that component. This can be caused when a multiplexed component is enabled in the Cummins ECM, but the immobilizer anti-theft device source address of the VECU transmitting the component message is incorrect in the Cummins ECM, or the immobilizer anti-theft device is not setup to transmit the multiplexed component message.
2)This fault can be caused by a bad J1939 datalink connection between the immobilizer anti-theft device and Cummins ECM , a bad connection between the component and the immobilizer anti-theft device, bad immobilizer anti-theft device or bad Cummins ECM. It may be necessary to contact the OEM for proper multiplexing configuration.

On-Board Diagnostics (OBD) Information:

1)The ECM illuminates the appropriate amber or red fault lamp when the diagnostic runs and fails.
2)The ECM turns off the appropriate fault lamp when the diagnostic runs and passes.

Possible repairs:

1)Repair/replace the OEM harness