Cummins fault code 2377 is documented on this DiagTechPro library page for Cummins ISM CM871 (2007-09) engines, where it flags a Fan Control Circuit condition (PID S033, SPN 647, FMI 3/3, Amber lamp). This 5-page PDF reproduces the manufacturer description, shop talk, component location and step-by-step troubleshooting so technicians can confirm and clear the code.
Cummins fault code 2377 overview
Cummins defines this code as “FAN CONTROL CIRCUIT – VOLTAGE ABOVE NORMAL, OR SHORTED TO HIGH SOURCE” on the Fan Control Circuit. The fan control circuit is a device used by the engine to control the fan operation. When the electronic 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. The diagnostic 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.
According to the shop talk notes, possible causes include:
- An open circuit in the engine harness or fan control solenoid.
- A short circuit to voltage source in the OEM harness.
- A damaged ECM.
Official document details
| Brand | Cummins |
| Model coverage | Cummins ISM CM871 (2007-09); Cummins ISX CM871 (2007-09) |
| System / Group | Fan Control Circuit — ISM CM871 fault codes |
| Fault code | 2377 (SPN 647, FMI 3/3) |
| Source | TruckFaultCodes.com Cummins fault code reference (© 2017) |
| Pages | 5 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code identification (PID, SPN, FMI, lamp)
- Description
- Shop Talk
- Component Location
- Troubleshooting Steps
Applicable truck models and engines
This document applies to Cummins ISM CM871 (2007-09); Cummins ISX CM871 (2007-09) equipped diesel engines that log Fault Code 2377. Always confirm engine calibration and use a Cummins diagnostic tool such as INSITE to read live data before starting repairs. Full specifications are published on the Cummins official website.
Who needs this Cummins fault code 2377 manual
Heavy-duty truck technicians, fleet workshops and owner-operators diagnosing an electronic control module warning on ISM CM871 engines will use this sheet to verify the fault before parts are replaced.
The full PDF is available in the DiagTechPro manuals library; a free account is required to download.
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