Massey Ferguson 4344.05 – Engine Control Unit (ECU): DEF Unit Internal Temperature Sensor Issue

There is an error in the exhaust SCR (Selective Catalytic Reduction) after-treatment system. The system is unable to properly read the temperature of the Diesel Exhaust Fluid (DEF) inside the DEF unit. FMI 05 indicates an open circuit or current below normal.

• 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

1. 1

   Inspect the wiring harness leading to the DEF supply module/pump and the DEF tank sensor for rubbed wires, broken connections, or corroded pins.

2. 2

   Visually inspect the DEF tank and pump module for signs of physical damage, freezing damage, or severe vibration stress.

3. 3

   Inspect the DEF fluid and tank cap/breather for dirt, water, or diesel contamination which can cause crystallization and damage internal sensors.

1. 1

   Stop Operation

   Stop driving the tractor as soon as possible to avoid greater damage, system blockages, and severe engine derate.

2. 2

   Isolate the Circuit

   Disconnect the battery or power to the ECU before servicing the DEF system.

3. 3

   Repair Wiring

   If the diagnostic checks revealed a broken wire or corroded connector at the DEF unit, repair the harness and reconnect it.

4. 4

   Replace the DEF Unit/Module

   If the wiring is intact, the internal temperature sensor itself has failed. Because this sensor is internal to the DEF supply module/tank unit and often non-serviceable on its own, the DEF Supply Module or Sensor Unit must be replaced.

5. 5

   Reassemble and Prime

   Install the new DEF supply module, ensuring all O-rings and quick connectors are seated properly to prevent air ingress.

6. 6

   Clear Codes

   Reconnect the battery, turn on the ignition, and use a compatible diagnostic scan tool to clear the fault code from the ECU.