Overview
| CODE | REASON | EFFECT |
| Fault Code: 3749 PID: SPN: 3226 FMI: 2/20 LAMP: Amber SRT: |
An offset in the outlet NOx sensor reading has been detected.
|
None on performance. |
Circuit Description
The aftertreatment outlet NOx (nitrogen oxides) sensor is a smart device and communicates with the engine control module (ECM) via the J1939 data link. The aftertreatment outlet NOx sensor performs its own internal diagnostics and reports malfunctions back to the primary ECM using the J1939 data link. The NOx sensor is permanently attached to the NOx control module. They are serviced as a single component and can not be replaced individually. The aftertreatment outlet NOx sensor is used to measure the NOx emissions at the outlet of the aftertreatment system.
Component Location
The aftertreatment outlet NOx sensor location can vary depending on engine application. It is usually located in the exhaust system at the outlet of the selective catalytic reduction (SCR) catalyst.
Conditions for Running the Diagnostics
This diagnostic consists of two parts:
This diagnostic runs when the aftertreatment SCR outlet temperature is above 200°C [392°F], and the engine is in a motoring condition.
Conditions for Setting the Fault Codes
The Engine Control Module (ECM) detected the aftertreatment outlet NOx sensor was not reading zero while in a motoring (non-fueling) condition.
Action Taken When the Fault Code is Active
- The ECM illuminates the amber CHECK ENGINE lamp and/or malfunction indicator lamp (MIL) after the diagnostic fails on two consecutive trips.
- This fault code may cause possible derate related fault code to become active.
Conditions for Clearing the Fault Code
- To validate the repair, start and operate the engine to raise exhaust temperatures. This can be done by either driving the vehicle or initiating a stationary regeneration using the recommended Cummins® electronic service tool or equivalent.
- The aftertreatment SCR outlet temperature must be above 200° C [392° F] for 60 seconds before the aftertreatment outlet NOx sensor can run its internal diagnostics.
- 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 immediately 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 causes of this fault code include:
Malfunctioning aftertreatment outlet NOx sensor
Diesel exhaust fluid crystallization or deposits
Improperly installed aftertreatment outlet NOx sensor.
Reference the appropriate OEM wiring diagram when troubleshooting circuits that utilize wiring supplied by the OEM.
For intermittent power supply and datalink 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.
Troubleshooting Summary
Solution: S00000252
Verification
Conditions
- Turn keyswitch ON.
- Connect the recommended Cummins® electronic service tool or equivalent.
Action
- Use the recommended Cummins® electronic service tool or equivalent to read the fault codes.
Specification
Before troubleshooting this fault code, troubleshoot any fault code that is active or has more than one inactive count within the last 25 engine operating hours from the following list:
- Aftertreatment NOx: 1885, 1887, 2771, 3232, 3446, 3583, 3649, 3681, 3682, 3725
- Aftertreatment diesel exhaust fluid system: 1681, 1682, 3574, 6485, 6486
Linked Solutions
- None
Repair
- Perform a search on the appropriate fault codes.
Validation
- None
Solution: S00000967
Verification
Conditions
- Turn keyswitch OFF.
Action
- Perform the Aftertreatment Diesel Exhaust Fluid Doser Pump Override Test.
Specification
- If the Aftertreatment Diesel Exhaust Fluid Doser Pump Override Test is not within specification, then proceed to the Repair section.
Linked Solutions
- None
Repair
- Clean or replace the aftertreatment diesel exhaust fluid dosing valve.
Validation
- Check ECM Calibration Revision History
- Use the recommended Cummins® electronic service tool or equivalent to find the current ECM code and revision number in the ECM.
- Compare the ECM code and revision number in the ECM to the calibration revisions listed in the ECM Calibration Revision History Database for applicable changes related to this fault code.
- Refer to ECM Calibration Revision History Database.
- Connect all components
- Connect the recommended Cummins® electronic service tool or equivalent.
- Operate the engine within the «Conditions for Clearing the Fault Code» found in the Overview section of the troubleshooting procedure.
- Verify that the fault code is no longer active.
Solution: S00000564
Verification
Conditions
- Turn keyswitch OFF.
Specification
- If any excessive aftertreatment diesel exhaust fluid deposits were found inside the decomposition tube, then a plugged or restricted aftertreatment decomposition tube has been detected.
- Proceed to Linked Solutions section for additional checks.
Validation
- Connect all components
- Connect the recommended Cummins® electronic service tool or equivalent.
- Disable the fault code.
- Operate the engine within the «Conditions for Clearing the Fault Code» found in the Overview section of the troubleshooting procedure.
- Verify that the fault code is no longer active.
- Check ECM Calibration Revision History
- Use the recommended Cummins® electronic service tool or equivalent to find the current ECM code and revision number in the ECM.
- Compare the ECM code and revision number in the ECM to the calibration revisions listed in the ECM Calibration Revision History Database for applicable changes related to this fault code.
- Refer to ECM Calibration Revision History Database.
Solution: S00000735
Verification
Conditions
- Turn keyswitch OFF.
- Reconnect all aftertreatment diesel exhaust fluid lines and electrical connectors to the dosing unit and aftertreatment diesel exhaust fluid tank if they have been previously disconnected during troubleshooting.
Action
- Remove the aftertreatment diesel exhaust fluid dosing valve.
- Perform the Aftertreatment Diesel Exhaust Fluid System Leak Test found under ECM Diagnostic Tests.
Specification
- If a line, fitting, connection, or dosing unit is leaking, then a malfunction has been detected in the aftertreatment diesel exhaust fluid system or dosing unit.
Linked Solutions
- None
Validation
- Connect all components
- Connect the recommended Cummins® electronic service tool or equivalent.
- Disable the fault code.
- Operate the engine within the «Conditions for Clearing the Fault Code» found in the Overview section of the troubleshooting procedure.
- Verify that the fault code is no longer active.
- Check ECM Calibration Revision History
- Use the recommended Cummins® electronic service tool or equivalent to find the current ECM code and revision number in the ECM.
- Compare the ECM code and revision number in the ECM to the calibration revisions listed in the ECM Calibration Revision History Database for applicable changes related to this fault code.
- Refer to ECM Calibration Revision History Database.
Solution: S00000443
Verification
Conditions
- Connect all components.
- Turn keyswitch ON.
- Connect the recommended Cummins® electronic service tool or equivalent.
Action
- Use the recommended Cummins® electronic service tool or equivalent to read the fault codes.
- Use the recommended Cummins® electronic service tool or equivalent to find the current ECM code and revision number in the ECM.
- Compare the ECM code and revision number in the ECM to the calibration revision listed in the ECM calibration revision history for applicable changes.
Specification
- If a calibration update for this fault code is available, the ECM calibration revision must be that revision or higher.
Linked Solutions
- None
Repair
- Prior to downloading the ECM calibration, check to see that all job images and all other troubleshooting has been documented as downloading an ECM calibration will remove the fault codes on the ECM.
- Download the updated ECM calibration code.
Validation
- Connect all components
- Connect the recommended Cummins® electronic service tool or equivalent.
- Disable the fault code.
- Operate the engine within the «Conditions for Clearing the Fault Code» found in the Overview section of the troubleshooting procedure.
- Verify that the fault code is no longer active.
- Check ECM Calibration Revision History
- Use the recommended Cummins® electronic service tool or equivalent to find the current ECM code and revision number in the ECM.
- Compare the ECM code and revision number in the ECM to the calibration revisions listed in the ECM Calibration Revision History Database for applicable changes related to this fault code.
- Refer to ECM Calibration Revision History Database.
Solution: S00000994
Verification
Conditions
- None
Action
- Verify all preceding solution verifications for this fault code have been performed.
Specification
- If the fault code is still active or inactive with more than one count within the last 25 engine hours and all the preceding solution verifications have been performed, then a malfunctioning aftertreatment outlet NOx sensor has been detected.
Linked Solutions
- None
Validation
- Connect all components
- Connect the recommended Cummins® electronic service tool or equivalent.
- Disable the fault code.
- Operate the engine within the «Conditions for Clearing the Fault Code» found in the Overview section of the troubleshooting procedure.
- Verify that the fault code is no longer active.
- Check ECM Calibration Revision History
- Use the recommended Cummins® electronic service tool or equivalent to find the current ECM code and revision number in the ECM.
- Compare the ECM code and revision number in the ECM to the calibration revisions listed in the ECM Calibration Revision History Database for applicable changes related to this fault code.
- Refer to ECM Calibration Revision History Database.
If all steps have been completed and no root cause has been identified, then follow the technical escalation process.