Massey Ferguson 3031.15 – ECU: DEF Tank Temperature Sensor Issue

The Engine Management System (EEM) has detected that the Diesel Exhaust Fluid (DEF) tank temperature sensor is reporting a value that is valid but above the normal operating range. This indicates a failing sensor, a wiring issue, or that the DEF tank is genuinely overheating due to a stuck-open engine coolant valve.

• 4710
• 7724S
• 5712SL
• 7722S
• 7722
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 4708
• 7726S
• 4707
• 4709
• 5711SL
• 7718S
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 7720
• Tier 4 (2015-2021)
• 7715S
• 7724
• 5608
• 5609
• 5610
• 5611
• 5612
• 5613
• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626
• 8600 Series

1. 1

   Check the Wiring Harness: Inspect the wiring harness and connector going to the DEF tank header unit. Look for loose contacts, corrosion, water ingress, or chafed wires.

2. 2

   Verify Actual Temperature: Use a diagnostic tool (like AGCO EDT) to read the live data from the DEF tank temperature sensor. Compare it to the ambient temperature (if the machine is cold) to see if the sensor is reading implausibly high.

3. 3

   Inspect the Coolant Control Valve: The DEF tank is heated by engine coolant to prevent freezing. If the reductant heater control valve (coolant valve) is stuck open, hot coolant will continuously flow through the DEF tank heating coil, causing the DEF fluid to genuinely overheat.

4. 4

   Check for Related Codes: Look for other active codes such as SPN 3031 FMI 3 (Voltage above normal/open circuit), FMI 4 (Voltage below normal), or FMI 16 (Temperature ABOVE normal).

1. 1

   Save and Erase Error Log

   Save the error log using your diagnostic tool, then erase it to see if the code returns immediately upon key-on.

2. 2

   Test the Coolant Valve

   If the live data shows the DEF tank is physically overheating during operation, test the coolant control valve. If it is stuck open, replace the valve.

3. 3

   Test the Sensor Circuit

   Disconnect the DEF tank header connector. Check for proper 5V reference and ground from the ECU. If the wiring is defective, repair the harness.

4. 4

   Replace the DEF Tank Header

   If the wiring and coolant valve are functioning correctly, the sensor itself has failed internally. Replace the entire DEF tank header unit.

5. 5

   Reassemble and Clear Codes

   Install the new DEF header, reconnect the harness, and clear the fault codes.

6. 6

   Validation Run

   Start the engine and run it on high idle for a few minutes. Turn the key off for 15 seconds, then restart and run on high idle again to ensure the code does not return and the ECU registers the new sensor.