Massey Ferguson 004344.05 – ECU: DEF Internal Temp Sensor Fault

The Engine Control Unit (ECU) has detected a problem with the internal temperature sensor of the DEF unit, indicating either an electrical fault (open or short circuit) or an implausible temperature reading. The ECU relies on this sensor to monitor DEF temperature, control heating elements to prevent freezing, and ensure accurate dosing. A failure in this sensor compromises the Selective Catalytic Reduction (SCR) system and can lead to reduced engine power, dashboard warning lights, and the vehicle entering limp mode to prevent emissions system damage.

• 5608
• 5609
• 5610
• 5611
• 5612
• 5613
• 5710SL
• 5711SL
• 5712SL
• 5713SL
• 7714
• 7715
• 7715S
• 7716
• 7716S
• 7718
• 7718S
• 7719
• 7720
• 7720S

1. 1

   Use a diagnostic scan tool to record the exact fault code and check for any other associated codes.

2. 2

   Visually inspect the wiring harness and connectors associated with the DEF tank and DEF supply module for damage, moisture intrusion, loose pins, or white crystalline DEF residue.

3. 3

   Test the DEF concentration with a refractometer (should be 32.5%) to ensure poor quality or contaminated DEF is not causing multiple SCR system issues.

4. 4

   Check for proper power (typically a 5V reference) and a good ground connection at the sensor's connector using a multimeter.

5. 5

   Disconnect the sensor and measure the resistance across its terminals. A reading of zero ohms indicates a short circuit, while an infinite reading (OL) suggests an open circuit.

6. 6

   Compare the measured resistance to specification (e.g., a typical automotive temperature sensor might read around 2,500 Ohms at 20°C/68°F and 300 Ohms at 80°C/176°F) to definitively identify an open or short circuit.

1. 1

   Confirm the fault

   Use a diagnostic scan tool to confirm that fault code 004344.05 is active or stored in the ECU.

2. 2

   Perform Diagnostic Checks

   Follow the diagnostic steps outlined above, starting with a visual inspection of the wiring and connectors for the DEF tank and pump assemblies.

3. 3

   Isolate the faulty component

   Based on the electrical tests, determine if the fault lies in the wiring harness or the sensor itself. If the wiring is faulty, repair or replace the damaged section.

4. 4

   Identify the sensor location

   Determine which sensor is triggering the fault. The SCR system typically has two temperature sensors: one integrated with the DEF level sender unit inside the tank, and another within the DEF supply (pumping) module.

5. 5

   Replace the faulty assembly

   If the sensor is determined to be faulty, replace the entire assembly it is part of (either the DEF tank sender unit or the DEF supply module), as the sensor is not available as a standalone part.

6. 6

   Clear Fault Codes

   After replacing the component, use a diagnostic scan tool to clear the fault code from the ECU.

7. 7

   Perform System Test

   Start the tractor and let it run to allow the ECU to verify that the fault has been resolved. Check for the recurrence of the fault code.