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SPN 3031 FMI 2

Aftertreatment 1 DEF Tank Temperature — 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: Temperature of the DEF in the tank, read by a sensor in the tank header. It controls tank heating and tells the computer whether the fluid can be pumped. More on SPN 3031.

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

A bad reading can block DEF heating or dosing and lead to inducement derates, especially in cold weather.

Likely causes

  1. Failed temperature sensor in the tank header (often combined with level/quality)
  2. DEF-corroded connector or wiring
  3. Tank heater fault making the reading implausible
  4. Network message missing from a smart tank sensor

Checks & fixes (easiest first)

  1. Compare the reading with ambient temperature after a cold soak
  2. Inspect the header connector for white crust and corrosion
  3. Check for related heater, level and quality codes
  4. Check for network codes if the sensor reports over CAN

FAQ

What does SPN 3031 FMI 2 mean?

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

Is SPN 3031 FMI 2 serious?

A bad reading can block DEF heating or dosing and lead to inducement derates, especially in cold weather.

What should I check first for SPN 3031 FMI 2?

Compare the reading with ambient temperature after a cold soak; Inspect the header connector for white crust and corrosion; Check for related heater, level and quality codes.