Massey Ferguson 4344.08 – Engine ECU: DEF Unit Internal Temperature Sensor Issue (ECU)

The engine management system has detected an abnormal signal, open circuit, or out-of-range voltage reading from the temperature sensor located inside the Diesel Exhaust Fluid (DEF / AdBlue) tank 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

1. 1

   Check for Active vs. Stored Codes: Connect a diagnostic service tool (like WinEEM4 or Jaltest) to save the error log and attempt to clear the code. If the code returns immediately upon key-on, the fault is active (hard failure).

2. 2

   Inspect the DEF Tank Header Wiring: Check the electrical connector at the top of the DEF tank (the DEF header unit). Look for corrosion, pushed-out pins, or moisture intrusion.

3. 3

   Test the Harness: Use a multimeter to check for continuity and verify the 12V/5V reference supply and ground between the DEF tank sensor connector and the Engine ECU.

4. 4

   Check for Contamination: Inspect the DEF fluid for dirt, diesel, or water contamination, which can foul the sensors inside the tank module.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the battery isolator switch to prevent electrical spikes.

2. 2

   Access the DEF Tank

   Locate the DEF tank assembly. Clean the area around the top of the tank thoroughly to prevent dirt from falling into the DEF fluid when the sensor is removed.

3. 3

   Disconnect Lines and Wiring

   Carefully unplug the electrical connector from the DEF header unit. Disconnect the heated DEF supply and return lines (be careful not to nick the O-rings on the quick connectors).

4. 4

   Remove the DEF Header/Sensor Unit

   The temperature sensor is typically integrated into the DEF tank header unit (which also houses the level and quality sensors). Unbolt or unscrew the retaining ring holding the header unit into the tank and carefully lift the assembly out.

5. 5

   Install the New Unit

   Insert the replacement DEF sensor/header unit into the tank. Secure the retaining ring.

6. 6

   Reconnect and Prime

   Reconnect the heated DEF lines and the electrical connector.

7. 7

   Clear Codes

   Reconnect the battery, turn the ignition on, and use a diagnostic tool to clear the 004344.08 fault code. Run the engine to verify the code does not return and that the system primes successfully.