Cummins ISB CM850 (2003-06) Fault Code: 1692 PID: SPN: 3234 FMI: 4 Aftertreatment NOx Sensor – Voltage Below Normal, or Shorted to Low Source. Out-of-range battery voltage has been detected by the aftertreatment outlet NOx sensor.

Posted by PerDiezel Solutions on January 18, 2026

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 voltage supplied to the aftertreatment outlet NOx sensor is below + 18-VDC
2)The voltage supplied to the aftertreatment outlet NOx sensor is above + 32-VDC
3)The aftertreatment outlet NOx sensor has malfunctioned or is damaged
4)The aftertreatment outlet NOx sensor internal heater has malfunctioned
5)The NOx sensor part number is incorrect.

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 cannot be cleared using INSITE? electronic service tool.
4)The fault code will be cleared from memory after 400 days or 9600 hours of engine operation.

Possible repairs:

1)Replace the NOXx sensor.
2)Replace the aftertreatment exhaust NOx sensor.
3)Clean the terminals and tighten the loose connections.
4)Repair or replace the OEM harness.
5)Replace the ECM.

Cummins ISB CM850 (2003-06) Fault Code: 1689 PID: 251 SPN: 251 FMI: 12 Real-Time Clock Power Interrupt – Data Erratic, Intermittent or Incorrect. The Real-Time clock power has been interrupted.

Cummins ISB CM850 (2003-06) Fault Code: 1687 PID: SPN: 3050 FMI: 0 Catalyst Over Temperature – Data Valid but Above Normal Operational Range – Most Severe Level. Very high temperatures have been detected in the aftertreatment system.

Cummins ISB CM850 (2003-06) Fault Code: 1684 PID: SPN: 3363 FMI: 4 Catalyst Tank Heater Circuit ? Voltage Below Normal, or Shorted to Low Source. Low signal voltage detected at the catalyst tank heater relay sensor circuit.

Cummins ISB CM850 (2003-06) Fault Code: 1683 PID: SPN: 3449 FMI: 3 Catalyst Tank Heater Circuit ? Voltage Above Normal, or Shorted to High Source. High signal voltage detected at the catalyst tank heater relay sensor circuit.

Cummins ISB CM850 (2003-06) Fault Code: 1682 PID: SPN: 3362 FMI: 11 Aftertreatment Diesel Exhaust Fluid Dosing Unit Input Lines – Condition Exists. An error has been detected by the catalyst dosing control unit.

Cummins ISB CM850 (2003-06) Fault Code: 1681 PID: SPN: 3361 FMI: 12 Catalyst Dosing Control Unit ? Bad Intelligent Device or Component. An internal error has been detected in the catalyst dosing control unit.

WARNING!