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SPN 3216 FMI 20

Aftertreatment 1 Intake NOx — Data drifted high.
The value has slowly crept higher than expected over time.

What the SPN covers: NOx sensor reading in the exhaust before the SCR catalyst (engine-out NOx). More on SPN 3216.

What FMI 20 usually points to: Sensor aging, contamination, or an offset problem. More on FMI 20.

Severity

MEDIUM — fix soon

Can lead to SCR efficiency codes and inducement derates if not repaired.

Likely causes

  1. Failed NOx sensor (common)
  2. Sensor not reaching operating temperature
  3. Exhaust leak near the sensor
  4. Network or power fault to the sensor module

Checks & fixes (easiest first)

  1. Check for exhaust leaks upstream of the sensor
  2. Check sensor power/ground and CAN wiring
  3. Compare inlet and outlet NOx readings
  4. Replace sensor per OEM test results

FAQ

What does SPN 3216 FMI 20 mean?

Aftertreatment 1 Intake NOx — data drifted high. The value has slowly crept higher than expected over time.

Is SPN 3216 FMI 20 serious?

Can lead to SCR efficiency codes and inducement derates if not repaired.

What should I check first for SPN 3216 FMI 20?

Check for exhaust leaks upstream of the sensor; Check sensor power/ground and CAN wiring; Compare inlet and outlet NOx readings.