Cummins ISB CM850 (2003-06) Fault Code: 1694 PID: SPN: 3234 FMI: 2 Aftertreatment Outlet NOx Sensor – Data Erratic, Intermittent, or Incorrect. An incorrect NOx sensor reading has been detected by the aftertreatment outlet NOx sensor.

Cummins ISB CM850 (2003-06) Fault Code: 1694 PID: SPN: 3234 FMI: 2 Aftertreatment Outlet NOx Sensor – Data Erratic, Intermittent, or Incorrect. An incorrect NOx sensor reading has been detected by 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) on the second consecutive ignition cycle that 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 cannot 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 ECM has detected that the NOx reading is higher or lower than is possible from the engine output.
2)Exhaust system leaks.
3)An incorrectly installed aftertreatment outlet NOx sensor.
4)An aftertreatment outlet NOx sensor that has carbon buildup on the tip of the sensor.
5)Excessive oil consumption.
6)Possible engine misfire
7)The NOx sensor part number is incorrect.

Possible repairs:

1)Replace the NOx? sensor.
2)Repair the NOx sensor installation and/or exhaust system.
3)Repair or replace the OEM wiring harness.
4)Replace the catalyst dosing unit.
5)Replace the ECM.