This fault code can only be caused by an internal ECM problem. Repairs are not possible for the ECM.
Possible repairs:
1)Replace the ECM.
Cummins ISB CM550 (1990-94) Fault Code: 111 PID: SID 254 SPN: 629 FMI: 12 Engine Control Module – critical internal failure. Error internal to the ECM related to memory hardware failures or internal ECM voltage supply circuits.
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