Massey Ferguson 4344.31 – ECU: DEF Unit Internal Temperature Sensor Issue

The engine management system has detected an implausible value, an abnormal rate of change, or a circuit error (such as an open or short circuit) from the temperature sensor located inside the Diesel Exhaust Fluid (DEF / AdBlue) unit.

• 4710
• 7724S
• 5712SL
• Interim Tier 4 (2012-2015)
• 7722
• 7722S
• 7615
• 5613
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 7616
• 7618
• 5608
• 4708
• 7619
• 7626
• 7726S
• 7624
• 4707
• 4709
• 5711SL
• 7614
• 7718S
• 5610
• 7620
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 5612
• 7622
• 7720
• Tier 4 (2015-2021)
• 5611
• 7715S
• 5609
• 7724
• MF 4707
• MF 4708
• MF 4709
• MF 4710
• MF 5608
• MF 5609
• MF 5610
• MF 5611
• MF 5612
• MF 5613
• MF 5710 SL
• MF 5711 SL
• MF 5712 SL
• MF 5713 SL
• MF 7614
• MF 7615
• MF 7616
• MF 7618
• MF 7619
• MF 7620
• MF 7622
• MF 7624
• MF 7626
• MF 7714
• MF 7715
• MF 7716
• MF 7716S
• MF 7718
• MF 7718S
• MF 7719
• MF 7720
• MF 7720S
• MF 7722
• MF 7722S
• MF 7724
• MF 7724S
• MF 7726
• MF 7726S

1. 1

   Check DEF Fluid Level: Top off the DEF tank first. Low DEF levels in high ambient temperatures can cause the tank temperature to spike rapidly, triggering temperature-related codes.

2. 2

   Inspect the Coolant Control Valve (CCV): Ensure the CCV (which routes hot engine coolant to the DEF tank heater) is not stuck open. A stuck-open valve will boil the DEF fluid. Conversely, check for frozen/slushy coolant in the lines during winter.

3. 3

   Electrical & Wiring Inspection: Inspect the wiring harness and the main connector at the DEF tank header. Look for rubbed wires, corrosion, or pushed-out pins.

4. 4

   Resistance Test: Using a multimeter, measure the resistance across the temperature sensor pins on the DEF header connector. Resistance should generally be under 1 MOhm and scale plausibly with the ambient temperature of the tank. An open circuit (infinite resistance) confirms a dead internal sensor.

1. 1

   Clean the Area

   Thoroughly wash and dry the top of the DEF tank. The SCR system is highly sensitive to contamination; even a grain of dirt or rust can destroy the DEF injector.

2. 2

   Depressurize and Disconnect

   Turn off the battery disconnect switch.

3. 3

   Remove Lines

   Carefully disconnect the DEF supply line, return line, and the two engine coolant lines attached to the header. Cap the lines immediately to prevent contamination and coolant loss.

4. 4

   Disconnect Electronics

   Unplug the main electrical harness connector from the DEF header.

5. 5

   Remove the Header

   Unscrew the locking ring or remove the mounting bolts securing the DEF header to the top of the tank.

6. 6

   Extract and Replace

   Carefully pull the old header assembly out of the tank. Insert the new DEF header assembly, ensuring the new rubber O-ring/gasket is seated perfectly to prevent water/dust ingress.

7. 7

   Reassembly

   Tighten the locking ring/bolts. Reconnect the coolant lines, DEF lines, and electrical harness.

8. 8

   Clear Codes

   Turn the battery switch back on, top off the tank with fresh AdBlue/DEF, and use a diagnostic service tool (like AGCO EDT) to clear the 004344.31 fault code and reset the SCR system adaptations.