Cummins ISL CM850 (2003-06) Fault Code: 1851 PID: SPN: 3249 FMI: 10 Exhaust Gas Temperature 2 ? Abnormal Rate of Change. The catalyst outlet temperature sensor is not responding to a change in engine operating conditions.

Cummins ISL CM850 (2003-06) Fault Code: 1851 PID: SPN: 3249 FMI: 10 Exhaust Gas Temperature 2 ? Abnormal Rate of Change. The catalyst outlet temperature sensor is not responding to a change in engine operating conditions.

The exhaust gas temperature #2 is monitored during engine warm-up. If the exhaust gas temperature 2 reading is not changing to match the engine operating conditions, the exhaust gas temperature 2 sensor is then determined to be stuck in-range and this fault code is logged. The ECM must not see engine speed for a period of eight hours before this diagnostic will run.

Possible causes:

1)Stuck in-range exhaust gas temperature #2 sensor reading
2)High resistance in the exhaust gas temperature #2 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 repairs:

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