Circuit DescriptionThe 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 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. INSITE™ electronic service tool can be used 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 can use a return that goes to the engine block or chassis ground.

Component LocationThe control solenoid location varies by OEM. Refer to the appropriate OEM service manual to determine the location.

Conditions for Running the DiagnosticsFor 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 PWM signal is less than 100 percent and will latch active when the fan PWM signal is 100 percent.

Conditions for Setting the Fault CodesThe Engine Control Module (ECM) detected the fan control circuit pulse width modulated (PWM) signal voltage was greater then 0-VDC when the PWM signal was commanded OFF.

Action Taken When the Fault Code is ActiveThe ECM illuminates the amber CHECK ENGINE lamp immediately when the diagnostic runs and fails.Fan operation will be disabled.Conditions for Clearing the Fault CodeTo validate the repair, perform a key cycle, and leave the key in the ON position for 1 minute.The fault code status displayed by INSITE™ electronic service tool will change to INACTIVE immediately after the diagnostic runs and passes.The ECM will turn off the amber CHECK ENGINE lamp immediately after the diagnostic runs and passes.The Reset All Faults command in INSITE™ electronic service tool can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications.

Shop TalkIf Fault Code 2377 is still active after completing all the steps in this fault code troubleshooting tree, consult the OEM service literature for procedures to check the fan clutch device for an open circuit or short circuit to ground.

Possible causes of this fault include:

An open circuit in the harness or fan control solenoid.A short circuit to voltage source in the OEM harness.A malfunctioning ECM.Reference the appropriate OEM wiring diagram when troubleshooting circuits that utilize wiring supplied by the OEM.

Possible Cause:1) Fan Control Solenoid failure2) OEM harness3) ECM failure