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SPN 3251 FMI 2

Aftertreatment 1 DPF Differential Pressure — Data erratic, intermittent, or incorrect.
The signal jumps around, drops in and out, or disagrees with other information the controller has.

What the SPN covers: Pressure difference across the diesel particulate filter — how hard the exhaust is working to push through it. More on SPN 3251.

What FMI 2 usually points to: Loose or corroded connectors, chafed wiring, a failing sensor, or two redundant sensors that do not agree. More on FMI 2.

Severity

MEDIUM — fix soon

High readings mean a loaded or plugged DPF. Regenerate or service soon to avoid a severe derate.

Likely causes

  1. DPF loaded with soot or ash
  2. Cracked or melted sensor hoses/tubes
  3. Faulty differential pressure sensor
  4. Failed regeneration due to other faults

Checks & fixes (easiest first)

  1. Inspect the sensor tubes for cracks, plugging or reversed lines
  2. Read soot load and perform a parked regen if allowed
  3. Check the sensor key-on, engine-off reading (should be near zero)
  4. Have the DPF cleaned or replaced if ash-loaded

FAQ

What does SPN 3251 FMI 2 mean?

Aftertreatment 1 DPF Differential Pressure — data erratic, intermittent, or incorrect. The signal jumps around, drops in and out, or disagrees with other information the controller has.

Is SPN 3251 FMI 2 serious?

High readings mean a loaded or plugged DPF. Regenerate or service soon to avoid a severe derate.

What should I check first for SPN 3251 FMI 2?

Inspect the sensor tubes for cracks, plugging or reversed lines; Read soot load and perform a parked regen if allowed; Check the sensor key-on, engine-off reading (should be near zero).