Cummins ISB 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...

Cummins ISB CM850 (2003-06) Fault Code: 1664 PID: SPN: 3050 FMI: 11 Catalyst Missing ? Condition Exists. The aftertreatment catalyst in the exhaust system is not present. This fault code becomes active when the inlet and outlet temperature sensors do not detect the presence of a catalyst in the aftertreatment system. This can be caused by tampering with the catalyst system, the catalyst has been removed from the vehicle, or a failed catalyst. 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. If...

Cummins ISB CM850 (2003-06) Fault Code: 1665 PID: SPN: 3241 FMI: 4 Exhaust Gas Temperature 1 Circuit ? Voltage Below Normal, or Shorted to Low Source. Low signal voltage detected at the catalyst inlet temperature sensor circuit. The catalyst inlet temperature sensor shares return wires in the engine harness with other sensors. A shorted return can cause multiple fault codes to be active. Possible causes: 1)Signal shorted to ground in the harness2)Signal shorted to return or ground in the sensor On-Board Diagnostics (OBD) Information (Euro 4 Certified Engines): 1)The ECM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs...

Cummins ISB CM850 (2003-06) Fault Code: 1666 PID: SPN: 3241 FMI: 3 Exhaust Gas Temperature 1 Circuit ? Voltage Above Normal, or Shorted to Low Source. High signal voltage detected at the catalyst inlet temperature sensor circuit Catalyst inlet temperature sensor shares return wires in the engine harness with other sensors. A shorted return can cause multiple fault codes to be active. Possible causes: 1)Open return circuit in the harness, connectors, or sensor.2)Open signal circuit or shorted to a voltage source. On-Board Diagnostics (OBD) Information (Euro 4 Certified Engines): 1)The ECM illuminates the malfunction indicator lamp (MIL) when the diagnostic...

Cummins ISB CM850 (2003-06) Fault Code: 1667 PID: SPN: 3241 FMI: 2 Exhaust Gas Temperature 1 ? Data Erratic, Intermittent, or Incorrect. The exhaust gas temperature #1 sensor is not changing with engine operating conditions. 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 #1 does not match the engine operating conditions, this fault code is logged. Possible causes: 1)Stuck in-range exhaust gas temperature #1 sensor2)High resistance in the exhaust...