Cummins ISB CM850 (2003-06) Fault Code: 426 PID: SID 231 SPN: 639 FMI: 2 SAE J1939 data link – cannot transmit. Communication between the ECM and another device on the SAE J1939 data link has been lost.

This fault occurs whenever the ECM starts communicating with any other device using the SAE J1939 data link and then can no longer transmit on the data link. Possible causes could be the following: Unplugging an electronic service tool before keying off the ECM, the SAE J1939 data link having an intermittent electrical problem, and the ECM (or another SAE J1939 device) tying up communications because of an electrical problem or by sending too many messages without stopping.

Possible repairs:

1)Repair the damaged harness, connectors, or pins if possible.