Cummins ISL CM850 (2003-06) Fault Code: 1663 PID: SPN: 3241 FMI: 11 Catalyst Inlet Temperature Sensor Swapped with Outlet ? Condition Exists. The inlet and outlet catalyst temperature sensor connections are swapped.

Both inlet and outlet exhaust gas temperature sensors have the same part number, so it is possible to get the sensors connected backwards to the engine harness. This fault code is activated when the ECM determines that the temperature reading from the inlet and outlet sensors are reading backwards. The most likely cause of this fault code is that the inlet and exhaust temperature sensor connectors are swapped at the engine harness. Disconnect the inlet and outlet temperature sensors from the engine harness and swap the connectors. The catalyst temperature sensors must be reading ambient temperature and the engine must be off for a period of eight hours before this diagnostic will run.

On-Board Diagnostic (OBD) Information:

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 the memory after 40 consecutive drive cycles when the diagnostic runs and passes.

Possible repairs:

1)The catalyst inlet and catalyst exhaust temperature sensor readings are swapped. Swap the wiring harness connections to the exhaust gas temperature 1 sensor and catalyst exhaust temperature sensor.