Massey Ferguson E4344.08 – Engine Control Unit (ECU): DEF Unit Internal Temperature Sensor Issue (ECU)

System is receiving an implausible reading, an open circuit, or a short circuit from the temperature sensor located inside the Diesel Exhaust Fluid (DEF / AdBlue) unit. The SCR system relies on this sensor to determine if the DEF is frozen or at optimal operating temperature for injection.

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

1. 1

   Visual Inspection: Inspect the DEF tank and the DEF pump/sensor module for physical damage. Ensure the tank cap and breather are intact, as dirt or water ingress can ruin the sensor.

2. 2

   Wiring and Connectors: Check the electrical harness connecting to the DEF tank header and DEF pump. Look for chafed wires, corrosion inside the connector pins, or loose connections, which frequently cause false sensor faults.

3. 3

   Live Data Verification: Use a diagnostic tool (such as AGCO Tech Connect) to read the live DEF temperature. If the sensor reads a constant extreme value (e.g., -40°C or +150°C), the sensor has failed internally or there is a hard wiring fault.

4. 4

   Fluid Quality Check: Ensure the DEF fluid is clean and uncontaminated (no diesel or water mixed in). Bad fluid can sometimes trigger cascading sensor errors.

1. 1

   Preparation

   Turn off the tractor, remove the key, and disconnect the battery to prevent electrical shorts.

2. 2

   Clean the Area

   Thoroughly clean the top of the DEF tank and around the DEF unit. The SCR system is highly sensitive to contamination; treat the area like a fuel system.

3. 3

   Disconnect Lines

   Carefully disconnect the electrical harness from the DEF unit. Disconnect the DEF supply and return lines. Tip: Cap the lines immediately to prevent dirt ingress and wipe up any spilled DEF with warm water to prevent crystallization.

4. 4

   Remove the Unit

   Unscrew the retaining ring or mounting bolts securing the DEF sensor/pump module to the tank. Carefully lift the unit out of the tank.

5. 5

   Installation

   Insert the new DEF sensor/pump unit, ensuring the new O-ring/gasket is properly seated to prevent leaks. Tighten the retaining ring or bolts to OEM torque specs.

6. 6

   Reconnection

   Remove the caps and reconnect the DEF fluid lines (ensure quick-connects click into place) and plug in the electrical harness.

7. 7

   Final Steps

   Reconnect the battery. Fill the tank with fresh, ISO 22241 certified DEF. Use a diagnostic tool to clear the E4344.08 fault code and run a DEF system prime/test to ensure there are no leaks and the temperature is reading correctly.