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.

Posted by PerDiezel Solutions on January 18, 2026

Fault code 1681 is triggered when the Dosing Control Unit has detected an internal error. The only troubleshooting that can be done is to recalibrate the engine ECM. If fault code 1681 is still active after the engine ECM has been recalibrated, the Dosing Control Unit will need to be replaced.

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

1)The ECM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
2)The ECM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. The MIL lamp and fault code can also be cleared using the INSITE? service tool.
3)The fault code will be cleared from memory after 40 consecutive drive cycles where the diagnostic runs and passes.

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 the INSITE? 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 dosing control unit.
2)Replace the ECM.

Cummins ISB CM850 (2003-06) Fault Code: 1679 PID: SPN: 3031 FMI: 2 Catalyst Tank Temperature ? Data Erratic, Intermittent, or Incorrect. The catalyst solution temperature sensor is not changing with engine operating conditions.

Cummins ISB CM850 (2003-06) Fault Code: 1678 PID: SPN: 3031 FMI: 3 Catalyst Tank Temperature ? Voltage Above Normal, or Shorted to High Source. High signal voltage or open circuit detected at the catalyst tank temperature sensor circuit

Cummins ISB CM850 (2003-06) Fault Code: 1677 PID: SPN: 3031 FMI: 4 Catalyst Tank Temperature ? Voltage Below Normal, or Shorted to Low Source. Low signal voltage detected at the catalyst solution temperature sensor circuit.

Cummins ISB CM850 (2003-06) Fault Code: 1676 PID: SPN: 3249 FMI: 2 Exhaust Gas Temperature 2 ? Data Erratic, Intermittent, or Incorrect. The exhaust gas temperature #2 sensor is not changing with engine operating conditions.

Cummins ISB CM850 (2003-06) Fault Code: 1675 PID: SPN: 3249 FMI: 3 Exhaust Gas Temperature 2 Circuit ? Voltage Above Normal, or Shorted to Low Source. High signal voltage detected at the catalyst outlet temperature sensor circuit.

Cummins ISB CM850 (2003-06) Fault Code: 1674 PID: SPN: 3249 FMI: 4 Exhaust Gas Temperature 2 Circuit ? Voltage Below Normal, or Shorted to Low Source. Low signal voltage detected at the catalyst exhaust temperature sensor circuit.

WARNING!