Cummins ISB CM850 (2003-06) Fault Code: 2771 PID: SPN: 3234 FMI: 9 Aftertreatment Outlet NOx Sensor – Abnormal Update Rate. No communications or valid data transfer rate detected on the J1939 datalink between the ECM and the aftertreatment outlet NOx sensor.

On-Board Diagnostics (OBD) Information (Euro 4 Stage 1+ Certified Engines):

1)The ECM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
2)An engine torque derate will be activated after 50 hours of engine operation with the fault code active.
3)The ECM turns OFF the malfunction indicator lamp (MIL) after 1 ignition cycle that the diagnostic runs and does not fail. The MIL lamp can not be cleared using the INSITE? electronic service tool.
4)The fault code will be cleared from memory after 400 days or 9600 hours of engine operation.

The NOx sensor is permanently attached to the NOx control module. They are serviced as a single component and can not be replaced individually.

Possible causes:

1)The aftertreatment outlet NOx sensor is not receiving power from the battery supply circuit in the OEM harness. This could be caused by an open circuit in the power supply wire, blown NOx sensor fuse, or low voltage supplied by the battery.
2)Open return circuit on the aftertreatment outlet NOx sensor circuit between the battery circuit aftertreatment outlet NOx sensor.
3)Open or short circuit on the J1939 datalink circuit between the engine ECM and aftertreatment outlet NOx sensor.
4)Intermittent communications between the aftertreatment outlet NOx sensor and the primary engine ECM on the J1939 datalink.
5)A damaged engine ECM
6)Incorrect engine calibration.

Possible repairs:

1)Replace the NOx? sensor.
2)Replace the aftertreatment outlet NOx sensor.
3)Tighten the loose connections, and clean the terminals.
4)Repair or replace the OEM harness
5)Repair or replace the terminating resistor in the OEM harness.
6)If necessary, calibrate the ECM.