Cummins Fault Code
Free · no signupCummins 6254 (SPN:6254 / FMI:9)
Limp Mode / Engine Derate.
System
Aftertreatment
Symptom
Limp Mode / Engine Derate.
Diagnosis & fix steps
LOGIC: Abnormal Update Rate (FMI 9) for the Aftertreatment Outlet NOx Sensor via J1939.
ACTION: Check the 4-pin connector at the outlet NOx sensor for power/ground; inspect the J1939 data link for a break.
Red Seal field insights
Pro-Tip: Don't just replace the sensor. This is a "Communication" fault, not a "Reading" fault. If the sensor loses its 24V supply (due to a blown fuse or corroded wire), the ECM loses the "heartbeat" and trips 6254.
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