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.

This diagnostic runs when the engine has not been running for at least eight hours. The catalyst solution temperature sensor is compared to engine coolant temperature and intake manifold temperature when the key is turned on after the extended eight hour shutdown. This fault code is logged if the reading from the catalyst solution temperature sensor does not match the readings from engine coolant temperature and intake manifold temperature.

Possible causes:

1)Stuck in-range catalyst solution temperature sensor
2)High resistance in the catalyst solution temperature sensor signal or return lines.

On-Board Diagnostics (OBD) Information (Euro 4 and 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)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 epairs:

1)Replace the catalyst solution temperature sensor.
2)Repair or replace the engine harness.
3)Replace the ECM.