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.

Posted by PerDiezel Solutions on January 18, 2026

Catalyst outlet temperature sensor shares return wires in the engine harness with other sensors. A shorted return can cause multiple fault codes to be active.

Possible causes:

1)Open return circuit in the harness, connectors, or sensor.
2)Open signal circuit or shorted to a voltage source.

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 exhaust gas temperature #2 sensor.
2)The removal and installation of the connector may correct the problem.
3)Repair or replace the engine harness.
4)Replace the ECM.

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.

Cummins ISB CM850 (2003-06) Fault Code: 1673 PID: SPN: 1761 FMI: 1 Catalyst Tank Level ? Data Valid but Below Normal Operational Range ? Most Severe Level. No catalyst solution has been detected in the catalyst solution tank.

Cummins ISB CM850 (2003-06) Fault Code: 1671 PID: SPN: 1761 FMI: 1 Catalyst Tank Level ? Data Valid but Below Normal Operational Range ? Moderately Severe Level. Low catalyst solution level has been detected in the catalyst solution tank.

Cummins ISB CM850 (2003-06) Fault Code: 1669 PID: SPN: 1761 FMI: 3 Catalyst Tank Level Sensor Circuit ? Voltage Above Normal, or Shorted to High Source. High signal voltage detected at the catalyst tank level sensor circuit.

Cummins ISB CM850 (2003-06) Fault Code: 1668 PID: SPN: 1761 FMI: 4 Catalyst Tank Level Sensor Circuit ? Voltage Below Normal, or Shorted to Low Source. Low signal voltage detected at the catalyst tank level sensor circuit.

Cummins ISB CM850 (2003-06) Fault Code: 1667 PID: SPN: 3241 FMI: 2 Exhaust Gas Temperature 1 ? Data Erratic, Intermittent, or Incorrect. The exhaust gas temperature #1 sensor is not changing with engine operating conditions

WARNING!