Cummins ISB CM850 (2003-06) Fault Code: 1683 PID: SPN: 3449 FMI: 3 Catalyst Tank Heater Circuit ? Voltage Above Normal, or Shorted to High Source. High signal voltage detected at the catalyst tank heater relay sensor circuit.

This fault code cannot detect any circuit failures on the heater side of the relay. Only circuit errors between the ECM and the relay can be detected by this fault code.

Possible causes:

1)Catalyst tank heater relay signal wire not connected to the relay
2)Catalyst tank heater relay return wire not connected to the relay
3)Faulty catalyst tank heater relay
4)Open circuit in the catalyst tank heater relay signal wire
5)Open circuit in the catalyst tank heater relay return wire
6)Catalyst tank heater signal wire shorted to a voltage source.

On-Board Diagnostics (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 memory after 40 consecutive drive cycles where the diagnostic runs and passes.

Possible repairs:

1)Replace the catalyst tank heater relay.
2)Repair or replace the engine harness.
3)The removal and installation of the connector may correct the problem.
4)Replace the ECM.