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SPN 3936 FMI 15

Aftertreatment 1 DPF System — Value too high (least severe).
The reading is above normal, but only at the lowest warning level.

What the SPN covers: A summary fault for the diesel particulate filter system, usually set when regenerations are not keeping soot under control. More on SPN 3936.

What FMI 15 usually points to: An early warning: mild over-temperature or over-pressure, or a sensor starting to drift high. More on FMI 15.

Severity

HIGH — limit use, diagnose now

Often comes with escalating derates. Fix the cause and regenerate before the DPF overloads.

Likely causes

  1. Regeneration requested but not completed
  2. Exhaust temperature sensor or DOC problem stopping regen
  3. Cracked or plugged DP sensor hoses
  4. Engine making excess soot
  5. Ash-loaded DPF needing cleaning

Checks & fixes (easiest first)

  1. Review regen history (frequency, completed vs. aborted)
  2. Check the exhaust temperature sensors and DOC light-off during a parked regen
  3. Inspect DP sensor tubes and hoses inside and out
  4. Have the DPF cleaned or weighed if ash-loaded

FAQ

What does SPN 3936 FMI 15 mean?

Aftertreatment 1 DPF System — value too high (least severe). The reading is above normal, but only at the lowest warning level.

Is SPN 3936 FMI 15 serious?

Often comes with escalating derates. Fix the cause and regenerate before the DPF overloads.

What should I check first for SPN 3936 FMI 15?

Review regen history (frequency, completed vs. aborted); Check the exhaust temperature sensors and DOC light-off during a parked regen; Inspect DP sensor tubes and hoses inside and out.