ISX12/ISX11.9 CM2250 Fault Code: 3751 | SPN: 4792 | FMI: 7Aftertreatment SCR Catalyst System – Mechanical System Not Responding or Out of Adjustment

Overview

Circuit Description

The engine control module (ECM) monitors the NOx concentration in the engine’s exhaust gases using an aftertreatment intake NOx sensor and an aftertreatment outlet NOx sensor. By comparing these two values, the ECM is able to determine the conversion efficiency of the SCR catalyst and dosing system.

Component Location

The SCR catalyst is located in the vehicle’s exhaust system, after the diesel particulate filter and decomposition tube.

Conditions for Running the Diagnostics

This diagnostic only runs during the recommended Cummins® electronic service tool or equivalent Aftertreatment Diesel Particulate Filter (DPF) Regeneration Test.

Conditions for Setting the Fault Codes

The Engine Control Module (ECM) detected the NOx conversion across the SCR catalyst was less than expected, indicating a malfunctioning SCR catalyst.

Action Taken When the Fault Code is Active

• The ECM logs the fault code immediately when the diagnostic runs and fails.

Conditions for Clearing the Fault Code

• 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

NOTE: This fault code is only used to assist in troubleshooting Fault Codes 3151, 3543, and/or 3582.