SPN 3216 FMI 21 is the Detroit DD Series fault-code procedure for an SCR inlet NOx sensor drift low-box fault. This 2-page diagnostic PDF documents the fault, its monitored circuit on the SCR inlet 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) | 3216 |
| FMI (failure mode) | 21 |
| Emission family | GHG14 calibration |
| Source | Detroit Power Service Literature (Copyright © 2017) |
| Pages | 2 |
| File size | 0.27 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code identification (SPN 3216, failure mode 21)
- Fault description and enabling conditions
- Troubleshooting steps
- Idle speed balance test and high-idle regeneration
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 3216 FMI 21 manual
Diesel technicians, fleet workshops and mobile mechanics diagnosing an SCR inlet NOx sensor drift low-box code on GHG14 Detroit engines need this reference to test the circuit correctly with a diesel diagnostic tool instead of replacing parts by guesswork.
SPN 3216 FMI 21 repair steps explained
This monitored engine-out NOx drift fault runs when EGR mass flow, engine speed of 1450-1900 rpm, torque, battery voltage, coolant and ambient temperature and barometric pressure conditions are met. The technician repairs any Exhaust Gas Recirculation (EGR) faults first, inspects the air inlet, Charge Air Cooler (CAC) and EGR piping for leaks, runs an idle speed balance (ISB) test to find a faulty fuel injector, checks the Aftertreatment System (ATS) for leaks, then performs a high-idle regeneration and submits the log to the Detroit Customer Support Center at 800-445-1980 per Power Service Literature.
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