Deutz-Fahr SPN 3031 FMI 3 – Engine Control Unit (ECU) / Aftertreatment Control Module (ACM / DCU): DEF (AdBlue) Tank Temperature Sensor - Voltage Above Normal, Or Shorted To High Source

The engine control system is receiving a maximum voltage signal from the DEF tank temperature sensor, meaning the circuit is broken (unplugged, cut wire, or internally failed sensor) or shorted to a power source.

• Agrotron Series 6 (6120 to 6210 TTV)
• Agrotron Series 7 (7200, 7250 TTV)
• Agrotron Series 9 (9340 TTV)
• 5C Series
• 5G Series

1. 1

   Visual Inspection: Locate the DEF tank header unit (sending unit) on top of the AdBlue tank. Disconnect the electrical connector and inspect for spread, corroded, or pushed-out pins.

2. 2

   Voltage Check: Turn the ignition ON (Engine OFF). Measure the voltage at the harness-side connector for the temperature sensor signal pin to ground. If it reads system voltage (e.g., 12V/24V) when it should be a 5V reference, there is a short to battery power in the wiring harness.

3. 3

   Resistance/Continuity Check: Turn the ignition OFF. Measure the resistance across the temperature sensor pins directly on the DEF header unit. If the multimeter reads 'OL' (Open Loop / infinite resistance), the internal temperature sensor has failed and the unit must be replaced.

4. 4

   Harness Check: Check continuity between the sensor connector and the ACM/ECU pins to rule out a broken wire in the chassis harness.

1. 1

   Preparation

   Park the machine on level ground, turn off the ignition, and disconnect the battery to prevent electrical shorts and disable the DEF pump.

2. 2

   Clean the Area

   Thoroughly clean the top of the DEF tank around the header unit. DEF systems are highly sensitive to dirt and contamination.

3. 3

   Disconnect Lines

   Mark and disconnect the DEF suction, return, and coolant heating lines (if equipped) from the header unit. Note: Coolant lines may leak; have a catch pan ready.

4. 4

   Remove the Unit

   Unscrew the retaining ring or mounting bolts securing the header unit to the tank. Carefully pull the header unit straight up and out of the tank, taking care not to bend the float or damage the suction tube.

5. 5

   Install New Unit

   Lubricate the new O-ring/seal with a small amount of clean DEF fluid (do not use grease or oil). Insert the new DEF header unit into the tank and secure the retaining ring/bolts.

6. 6

   Reassembly

   Reconnect all DEF lines, coolant lines, and the electrical connector.

7. 7

   Clear Codes

   Reconnect the battery, turn the ignition on, and use a diagnostic tool (such as Deutz SERDIA) to clear the SPN 3031 fault code and verify that the DEF temperature reading is now plausible.