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SPN 3226 FMI 13

Aftertreatment 1 Outlet NOx — Out of calibration.
The component or the controller's calibration for it is not within the expected range.

What the SPN covers: NOx sensor reading in the exhaust after the SCR catalyst (tailpipe NOx). More on SPN 3226.

What FMI 13 usually points to: A replaced part that needs a calibration or learn procedure, wrong software, or a worn component. More on FMI 13.

Severity

MEDIUM — fix soon

A bad outlet sensor often triggers SCR efficiency faults and derates.

Likely causes

  1. Failed NOx sensor
  2. Real high NOx from poor DEF dosing
  3. Exhaust leak
  4. Sensor wiring or module fault

Checks & fixes (easiest first)

  1. Check DEF quality and dosing
  2. Check for exhaust leaks
  3. Check sensor wiring and power
  4. Run the OEM SCR performance test

FAQ

What does SPN 3226 FMI 13 mean?

Aftertreatment 1 Outlet NOx — out of calibration. The component or the controller's calibration for it is not within the expected range.

Is SPN 3226 FMI 13 serious?

A bad outlet sensor often triggers SCR efficiency faults and derates.

What should I check first for SPN 3226 FMI 13?

Check DEF quality and dosing; Check for exhaust leaks; Check sensor wiring and power.