The Cummins ISX code 3751 manual is a 6-page PDF that documents fault code 3751, the aftertreatment SCR catalyst system fault reported as mechanical system not responding or out of adjustment. It explains that the ECM compares intake and outlet NOx readings to judge SCR conversion efficiency, and that this code is set when conversion across the catalyst is lower than expected, indicating a malfunctioning SCR catalyst. The procedure is credited to TruckFaultCodes.com and covers the circuit description, component location and full troubleshooting steps.
Official document details
| Brand | Cummins |
| Model coverage | Cummins ISX11.9 CM2250 and ISX12 CM2250 (2010-12) engines |
| System / group | ISX11.9 CM2250 (2010-12) / DTCs |
| Fault code | 3751 (SPN 4792, FMI 7) |
| Warning lamp | None |
| Pages | 6 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code 3751 description
- Circuit description and ECM operation
- Component location
- Shop talk and possible causes
- Step-by-step troubleshooting flow
Applicable truck models
This diagnostic applies to Cummins ISX11.9 CM2250 and ISX12 CM2250 (2010-12) engines. The SCR catalyst is located in the exhaust system after the diesel particulate filter and decomposition tube. The reported cause is a malfunctioning SCR catalyst; the diagnostic runs during the INSITE regeneration test and there is no direct effect on performance. For engine data and authorised service, visit the Cummins official website.
Who needs this Cummins ISX code 3751 manual
Heavy-duty diesel technicians, fleet workshops and owner-operators reach for this manual when fault code 3751 is logged as an information event. It helps an emissions technician validate SCR conversion and confirm a failing catalyst before recommending replacement.
Download the ISX code 3751 PDF
The complete procedure, wiring detail and step tables are available in the DiagTechPro manuals library; a free account is required to download the PDF. Keep it alongside the related ISX11.9 CM2250 fault-code sheets listed below.
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