This Cummins 3749 NOx Sensor document is a troubleshooting procedure for Fault Code 3749 on CM2250 engines. It explains an aftertreatment outlet NOx sensor data-not-rational condition, where the outlet NOx sensor reading has drifted high. The procedure covers fault-code checks, sensor installation, DEF decomposition tube crystallization, ECM calibration, and fault clearing with INSITE™.
Official Cummins 3749 NOx Sensor document details
| Brand | Cummins |
| Model coverage | ISB6.7 CM2250, ISC8.3 and ISL9 CM2250, ISX11.9 CM2250, ISX15 CM2250 |
| System/Group | ISB6.7 CM2250 (2010-12) / DTCs; aftertreatment outlet NOx sensor |
| Publication no. | Associated bulletins shown: 4022254, 4022257, 4022250, 2883445 |
| Year/Revision | Last modified 13-Sep-2010 and 25-Aug-2010; file year unknown |
| Pages | 8 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- Overview
- Circuit Description
- Component Location
- FAULT CODE 3749
- Conditions for Running the Diagnostics
- Conditions for Setting the Fault Codes
- Action Taken When the Fault Code is Active
- Conditions for Clearing the Fault Code
- Shop Talk
- Associated Procedures
- Troubleshooting Steps
- Guided Step 1 – Check the fault codes.
- Guided Step 1C – Verify proper installation of the aftertreatment outlet NOx sensor.
- Guided Step 2 – Check the aftertreatment diesel exhaust fluid decomposition tube.
- Guided Step 3 – Check ECM calibration and clear fault codes.
Applicable truck models
This procedure applies to Cummins CM2250 engine families listed in the document: ISB6.7 CM2250, ISC8.3 and ISL9 CM2250, ISX11.9 CM2250, and ISX15 CM2250. The fault concerns the aftertreatment outlet NOx sensor, a smart device communicating with the ECM over the J1939 data link and normally located at the outlet of the aftertreatment SCR catalyst. The document states that the NOx sensor and NOx control module are serviced as one component. For manufacturer information, visit Cummins official website.
Who needs this Cummins 3749 NOx Sensor manual
Workshop owners, diesel technicians, and fleet mechanics need this file when an amber CHECK ENGINE lamp or MIL is tied to SPN 3226 FMI 20. It gives the diagnostic sequence for checking active codes, related faults 1887, 2771, 3583, or 3681, outlet sensor installation, decomposition tube deposits, and ECM calibration status.
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