CM850 Electronic Control System – FAULT CODE 1663

Catalyst Inlet Temperature Sensor Swapped with Outlet – Condition Exists.


Fault Code: 1663
SPN: 3241
FMI: 11/31
LAMP: Amber

Catalyst Inlet Temperature Sensor Swapped with Outlet — Condition Exists. The inlet and outlet catalyst temperature sensor connections are swapped.

Catalyst solution injection into the aftertreatment system is disabled.


Circuit Description

The catalyst temperature sensors are used to monitor the temperatures of the exhaust gas entering and exiting the catalyst.

Component Location

The inlet and exhaust temperature sensors are located in the aftertreatment system. The inlet temperature sensor is located before the catalyst and the exhaust temperature sensor is located at the outlet of the exhaust.

Shop Talk

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:

  • The ECM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails
  • 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
  • The fault code will be cleared from the memory after 40 consecutive drive cycles when the diagnostic runs and passes.

Refer to Troubleshooting Fault Code t05-1663

Last Modified:  08-Jul-2010