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SPN 3226 FMI 10

Aftertreatment 1 Outlet NOx — Abnormal rate of change.
The value is changing faster than is physically believable.

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

What FMI 10 usually points to: Intermittent wiring, a sensor glitch, or a sudden real event such as a burst hose. More on FMI 10.

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 10 mean?

Aftertreatment 1 Outlet NOx — abnormal rate of change. The value is changing faster than is physically believable.

Is SPN 3226 FMI 10 serious?

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

What should I check first for SPN 3226 FMI 10?

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