SPN 3226 — Aftertreatment 1 Outlet NOx
System: Aftertreatment / SCR
NOx sensor reading in the exhaust after the SCR catalyst (tailpipe NOx).
Can I keep running it?
MEDIUM — fix soon
A bad outlet sensor often triggers SCR efficiency faults and derates.
Likely causes
- Failed NOx sensor
- Real high NOx from poor DEF dosing
- Exhaust leak
- Sensor wiring or module fault
Checks & fixes (easiest first)
- Check DEF quality and dosing
- Check for exhaust leaks
- Check sensor wiring and power
- Run the OEM SCR performance test
Common FMIs with SPN 3226
- SPN 3226 FMI 2Data erratic, intermittent, or incorrect
- SPN 3226 FMI 4Voltage below normal or shorted low
- SPN 3226 FMI 10Abnormal rate of change
- SPN 3226 FMI 12Bad intelligent device or component
- SPN 3226 FMI 13Out of calibration
- SPN 3226 FMI 20Data drifted high
Related codes
- SPN 3216Aftertreatment 1 Intake NOx
- SPN 4364Aftertreatment 1 SCR Conversion Efficiency
- SPN 3364Aftertreatment 1 DEF Quality
FAQ
What does SPN 3226 mean?
SPN 3226 is Aftertreatment 1 Outlet NOx. NOx sensor reading in the exhaust after the SCR catalyst (tailpipe NOx).
Can I keep running with SPN 3226?
A bad outlet sensor often triggers SCR efficiency faults and derates.
What causes SPN 3226?
Failed NOx sensor; Real high NOx from poor DEF dosing; Exhaust leak; Sensor wiring or module fault.