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SPN 3031 FMI 16

Aftertreatment 1 DEF Tank Temperature — Value too high (moderately severe).
The reading is above normal at a middle warning level — more serious than FMI 15, less than FMI 0.

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 16 usually points to: A developing over-condition that often precedes a derate. More on FMI 16.

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 16 mean?

Aftertreatment 1 DEF Tank Temperature — value too high (moderately severe). The reading is above normal at a middle warning level — more serious than FMI 15, less than FMI 0.

Is SPN 3031 FMI 16 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 16?

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.