Home › Codes › SPN 3031 › FMI 9

SPN 3031 FMI 9

Aftertreatment 1 DEF Tank Temperature — Abnormal update rate.
Expected data is arriving too slowly or has stopped arriving over the data link.

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 9 usually points to: A module that has dropped offline, a network wiring issue, or a module that is overloaded or resetting. More on FMI 9.

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. Check for other network codes and the module that sends this data
  2. Inspect the J1939 backbone and terminating resistors
  3. Compare the reading with ambient temperature after a cold soak
  4. Inspect the header connector for white crust and corrosion
  5. Check for related heater, level and quality codes
  6. Check for network codes if the sensor reports over CAN

FAQ

What does SPN 3031 FMI 9 mean?

Aftertreatment 1 DEF Tank Temperature — abnormal update rate. Expected data is arriving too slowly or has stopped arriving over the data link.

Is SPN 3031 FMI 9 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 9?

Check for other network codes and the module that sends this data; Inspect the J1939 backbone and terminating resistors; Compare the reading with ambient temperature after a cold soak.