Deutz-Fahr SPN 3031 FMI 4 – ACM (Aftertreatment Control Module): AdBlue (DEF) Tank Temperature Sensor - Voltage Below Normal, or Shorted to Low Source

The engine control system is receiving a signal voltage from the DEF tank temperature sensor that is below the minimum acceptable threshold. This typically indicates a short circuit to ground in the sensor wiring, a failed temperature sensor, or water intrusion in the connector.

• Deutz-Fahr 6 Series (6120, 6130, 6140, 6150, 6160, 6180, 6190 TTV)
• Deutz-Fahr 7 Series (Agrotron 7200, 7250 TTV)
• Deutz-Fahr 9 Series (Agrotron 9340 TTV)

1. 1

   Visually inspect the DEF tank header/sensor connector (both harness and sensor sides) for corrosion, bent pins, or water/DEF intrusion.

2. 2

   Measure resistance between the temperature sensor signal pin on the DEF tank connector and the ground pin to check for a short to ground in the wiring harness.

3. 3

   Measure resistance across the temperature sensor pins on the tank unit to verify if the sensor has failed internally (out of spec or dead short).

4. 4

   With the key ON and sensor disconnected, verify the ACM is supplying the correct 5V reference voltage to the sensor connector.

1. 1

   Disconnect Power

   Safely park the tractor, turn off the ignition, and disconnect the negative battery terminal.

2. 2

   Repair Wiring

   If the diagnostic checks revealed a short in the harness, trace the wiring back to the ACM (often a 120-pin connector) and repair or replace the damaged section of the wire.

3. 3

   Replace the DEF Tank Header

   Drain the AdBlue/DEF tank below the level of the sensor opening (or completely). Disconnect the electrical connector and the DEF suction/return lines from the top of the tank unit. Unscrew the retaining ring holding the DEF header unit to the tank. Carefully pull the old sensor unit out of the tank. Lubricate the new O-ring seal with a compatible lubricant (or distilled water) and insert the new DEF tank header unit. Tighten the retaining ring, reconnect the fluid lines, and plug in the electrical connector.

4. 4

   Clear Codes

   Reconnect the battery, refill the DEF tank, turn the key ON, and use a diagnostic scan tool to clear the SPN 3031 FMI 4 fault code. Run the engine to verify the code does not return.