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.

Posted by PerDiezel Solutions on January 18, 2026

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.

Cummins ISB CM850 (2003-06) Fault Code: 2376 PID: 412 SPN: 412 FMI: 2 Recirculation Exhaust Gas (EGR) Temperature Sensor Circuit – Voltage Below Normal or Shorted to Low Source. Low signal voltage detected at the EGR temperature circuit.

Cummins ISB CM850 (2003-06) Fault Code: 2375 PID: 412 SPN: 412 FMI: 3 EGR Temperature Sensor Circuit – Voltage Above Normal or Shorted to High Source. High signal voltage detected at the EGR temperature sensor circuit.

Cummins ISB CM850 (2003-06) Fault Code: 2374 PID: 95 SPN: 1209 FMI: 4 Exhaust gas pressure sensor circuit – shorted low. Low voltage detected on the exhaust gas pressure sensor exhaust circuit.

Cummins ISB CM850 (2003-06) Fault Code: 2373 PID: 95 SPN: 1209 FMI: 3 Exhaust gas pressure sensor circuit – shorted high. High voltage detected at the exhaust gas pressure sensor circuit.

Cummins ISB CM850 (2003-06) Fault Code: 2367 PID: SID 29 SPN: 1072 FMI: 3 Engine Brake Actuator Circuit #2 – Voltage Above Normal or Shorted to High Source. Open circuit or high voltage detected at the engine brake solenoid number 2 signal circuit.

Cummins ISB CM850 (2003-06) Fault Code: 2366 PID: SID 28 SPN: 1072 FMI: 3 Engine Brake Actuator Circuit #1 – Voltage Above Normal or Shorted to High Source. Open circuit or high voltage detected at the engine brake solenoid number 1 signal circuit.

WARNING!