Cummins Fault Code

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SPN 343 FMI 12

ECM Hardware Failure.

System

Electrical

Symptom

ECM Hardware Failure.

Diagnosis & fix steps

LOGIC: Internal ECM memory error (EEPROM). ACTION: Disconnect batteries for 30 mins to "Hard Reset." If it returns, the ECM requires a re-flash or replacement.

Red Seal field insights

Specs: Check for a "dirty" ground at the ECM block. PRO-TIP: Welding on the frame without disconnecting the ECM is the #1 cause of this internal hardware death.

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