Cummins Fault Code 6637

03/12/2025

Overview

CODE

REASON

EFFECT

Fault Code: 6637
PID:
SPN: 2978
FMI: 2/2
LAMP: Amber
SRT:

A loss of communication has been detected.

None on performance.

Cummins Fault Code 6637 — SAE J1939 Datalink Circuit

Circuit Description

Normally, switches, accelerators, and other components are connected to the engine control module (ECM) directly through individual wires. Multiplexing allows those same components to be hard wired to an original equipment manufacturer (OEM) vehicle electronic control unit (VECU) or transmission electronic control unit (ECU) in the cab. Then component values and states from components such as sensors, accelerators, and switches can be transmitted from the OEM VECU to the Cummins ECM over the SAE J1939 data link.

Messages sent from OEM VECUs or transmission ECUs are received by the Cummins ECM and used for controlling the engine. The Cummins ECM and OEM VECUs must be configured properly so that proper operation of the multiplexed components will occur.

Component Location

The SAE J1939 data link wiring and the SAE J1939 devices vary by OEM options.

Conditions for Running the Diagnostics

This diagnostic runs continuously when the keyswitch is in the ON position or when the engine is running.

Conditions for Setting the Fault Codes

The OEM VECU determines there is a malfunction of the multiplexed variable speed fan drive.

Action Taken When the Fault Code is Active

The ECM illuminates the amber CHECK ENGINE lamp and/or the malfunction indicator lamp (MIL) immediately when the diagnostic runs and fails.

Conditions for Clearing the Fault Code

To validate the repair, start the engine and let it idle for 1 minute.
The fault code status displayed by the recommended Cummins electronic service tool or equivalent will change to INACTIVE immediately after the diagnostic runs and passes.
The ECM will turn off the amber CHECK ENGINE lamp after the diagnostic runs and passes.
For On-Board Diagnostics (OBD) engines, the ECM will extinguish the Malfunction Indicator Lamp (MIL) after three consecutive trips where the diagnostic runs and passes.
The “Reset All Faults” command in the recommended Cummins electronic service tool or equivalent can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications.

Shop Talk

Possible cause of this fault code:

A malfunctioning SAE J1939 datalink circuit

Incorrect feature and parameter settings

For intermittent power supply and data link communication issues with aftertreatment components, it is highly recommended that the OEM Power Distribution Center fuses and relays be thoroughly checked for loose, missing, or intermittent connections.

XTuning.VN