SPN 3226 FMI 20 is the Detroit DD Series fault-code procedure for an SCR outlet NOx sensor drift-low fault. This 2-page diagnostic PDF documents the fault, its monitored circuit on the SCR outlet NOx sensor, and the exact troubleshooting steps a technician follows to confirm and repair the failure.
Official document details
| Brand | Detroit |
| Model coverage | DD Series (EPA 2007-Current); Series 60 DDEC VI |
| System / Group | DD Series / DTCs |
| SPN (fault code) | 3226 |
| FMI (failure mode) | 20 |
| Emission family | GHG14 calibration |
| Source | Detroit Power Service Literature (Copyright © 2017) |
| Pages | 2 |
| File size | 0.26 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code identification (SPN 3226, failure mode 20)
- Fault description and enabling conditions
- Troubleshooting steps
- High-idle regeneration and log submission
Applicable truck models
This procedure applies to Detroit DD13, DD15 and DD16 engines in the DD Series (EPA 2007-Current) range and the equivalent Series 60 (DDEC VI) platform, as fitted to Freightliner and Western Star trucks. Confirm the GHG14 emission family matches the truck before following the steps; full model and coverage data is published on the Detroit official website.
Who needs this SPN 3226 FMI 20 manual
Diesel technicians, fleet workshops and mobile mechanics diagnosing an SCR outlet NOx sensor drifting low on GHG14 Detroit engines need this reference to test the circuit correctly with a diesel diagnostic tool instead of replacing parts by guesswork.
SPN 3226 FMI 20 repair steps explained
This monitored engine-out NOx drift fault sets when fuel mass is 0, DPF outlet temperature is above 200 C, battery voltage is above 10 V DC and engine speed is 500-2100 rpm for more than 30 seconds. The technician checks the Aftertreatment System (ATS) for visible exhaust leaks or damage, connects a diesel diagnostic tool, disconnects the Diesel Exhaust Fluid (DEF) dosing unit, performs a high-idle regeneration, and submits the retained log file to the Detroit Customer Support Center at 800-445-1980. SPN 3361/5 is disregarded with the dosing unit unplugged.
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