SPN 3238 FMI 2 is the Detroit DD Series fault-code procedure for an SCR outlet NOx sensor failure to activate. This 3-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) | 3238 |
| FMI (failure mode) | 2 |
| Emission family | GHG14 calibration |
| Source | Detroit Power Service Literature (Copyright © 2017) |
| Pages | 3 |
| File size | 0.32 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code identification (SPN 3238, failure mode 2)
- Troubleshooting steps
- NOx conversion efficiency monitoring
- Parked regeneration verification
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 3238 FMI 2 manual
Diesel technicians, fleet workshops and mobile mechanics diagnosing an SCR outlet NOx sensor failing to activate on GHG14 Detroit engines need this reference to test the circuit correctly with a diesel diagnostic tool instead of replacing parts by guesswork.
SPN 3238 FMI 2 repair steps explained
The technician first confirms SPN 5357/FMI 16 or 18 is not present, then charts engine speed, SCR inlet and outlet temperatures, SCR inlet and outlet NOx sensor readings, and NOx conversion efficiency. The engine is started and a parked regeneration is performed; if NOx conversion efficiency rises above 70% (0.70) during the regeneration the faults are cleared and the vehicle released, otherwise the SCR outlet NOx sensor is replaced per Detroit Power Service Literature.
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