Cummins ISB CM850 (2003-06) Fault Code: 2377 PID: SID 33 SPN: 647 FMI: 3 Fan Control Circuit – Voltage Above Normal or Shorted to High Source. Open circuit or high voltage detected at the fan control circuit.

Cummins ISB CM850 (2003-06) Fault Code: 2377 PID: SID 33 SPN: 647 FMI: 3 Fan Control Circuit – Voltage Above Normal or Shorted to High Source. Open circuit or high voltage detected at the fan control circuit.

The ECM monitors the voltage level on this circuit. When the ECM commands the fan signal low, it expects the voltage level to be approximately 0 volts. If it detects a high voltage, this fault is recorded.

If Fault Code 2377 is still active after completing the following troubleshooting steps, consult the OEM service literature for procedures to check the fan clutch device for an open circuit or short circuit to ground.

Possible causes:

1)Open circuit in the engine harness or fan control solenoid
2)Short circuit to voltage source in the OEM harness
3)Failed ECM.

Possible repairs:

1)Replace the fan control solenoid.
2)Clean, repair or replace the OEM harness.
3) The removal and installation of the connector may correct the fault.
4)Replace the ECM.