Cummins ISM CM875 (2003-06) Fault Code: 343 PID: S254 SPN: 629 FMI: 12/12 Electronic Control Module Warning Internal Hardware Failure – Bad Intelligent Device or Component. ECM power supply errors have been detected.

This fault can also be caused by resistance in the ECM battery supply (+) or (-) circuits. Resistance in these circuits can cause the voltage level at the ECM input to drop low enough to set Fault Code 343 active.

Possible repair:

1)Replace the ECM.