Cummins ISB4.5 CM2150 Fault Code: 2377 PID: SID 33 SPN: 647 FMI: 3 Fan Control Circuit – Voltage Above Normal or Shorted to High Source.

Circuit Description
The fan control circuit is a device used by the engine to control the fan operation. When the engine control module (ECM) energizes the fan control circuit, the engine fan is engaged.

The fan control circuit utilizes a pulse width modulated (PWM) signal. A pulse width modulated (PWM) signal is a pulsed voltage signal between 0-VDC and system voltage. The frequency of the pulsed voltage signal is dependent on the application requirement.

There are two types of fans supported by the fan control circuit; variable speed and ON/OFF. Use INSITE™ electronic service tool to determine which fan type is currently set up for use. The fan control circuit varies by original equipment manufacturer (OEM). Certain OEMs can use a solenoid return that is wired to the ECM or goes to the engine block or chassis ground.

Component Location
The fan clutch solenoid location varies by OEM. Refer to the OEM service manual.

Conditions for Running the Diagnostics
For ON/OFF and variable speed fan types, the diagnostic runs when the fan is turned off and will latch active when the fan PWM signal is 100 percent. For all other fan types, the diagnostic runs when the fan pulse width modulated (PWM) signal is less than 100 percent and will latch active when the fan pulse width modulated (PWM) signal is 100 percent.

Conditions for Setting the Fault Codes
The fan control circuit PWM signal is detected to be greater than 0-VDC when the pulse width modulated (PWM) signal is turned off by the ECM.

Action Taken When the Fault Code is Active
-The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
-Fan operation will be disabled.

Conditions for Clearing the Fault Code
For ON/OFF and variable speed fan, the diagnostic will clear when the fan is turned off and the diagnostic runs and passes. For all other fan types, the diagnostic will clear when the fan pulse width modulated (PWM) signal is less than 100 percent.

Possible Causes
-An open circuit in the engine harness or fan control solenoid
-A short circuit to voltage source in the OEM harness
-A malfunctioning ECM.