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.

Posted by PerDiezel Solutions on January 18, 2026

This diagnostic runs when the exhaust gas temperature sensors are compared to other engine temperatures during engine operation. The engine coolant temperature must be above 140?F before the diagnostic will run. If the value of the exhaust gas temperature #2 does not match the engine operating conditions, this fault code is logged.

Possible causes:

1)Stuck in-range exhaust gas temperature #2 sensor
2)High resistance in the exhaust gas temperature #2 sensor signal or return lines.

On-Board Diagnostics (OBD) Information:

1)The ECM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that 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.

Possible repairs:

1)Replace the exhaust gas temperature #2 sensor.
2)Repair or replace the engine harness.
3)Replace the ECM.

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.

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.

WARNING!