Cummins Fault Code

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Cummins 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.

Same code keeps coming back?

That's a program problem, not a part problem. Book a 30-minute uptime review with Grant, a Red Seal Heavy Duty Technician.

Book an uptime review

Read before you touch anything

  • This is general reference information, not a repair manual. It is for trained, qualified technicians.
  • Fault codes, meanings and procedures vary by model, serial number and software version. Confirm the code and the procedure against the manufacturer's service manual before acting.
  • Follow the OEM service manual, torque specs and your site's safety procedures: lockout/tagout, block raised equipment, relieve hydraulic, fuel and air pressure, and let hot systems cool.
  • You use this information at your own risk. Adventure Mechanical and AM Fleet Integrity accept no liability for damage, injury, downtime or loss arising from its use.
  • Not affiliated with or endorsed by any manufacturer. Brand names are used only to identify the equipment a code applies to.

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