Massey Ferguson 4344.03 – Engine ECU: DEF Unit Internal Temperature Sensor Issue (ECU)

The DEF supply module's internal temperature measurement module is not responding or is defective. This will trigger a warning lamp, store a CAN message, and eventually lead to an engine power derate.

• 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
• 7714S
• 7719S

1. 1

   Clear the error log and restart the ECU/tractor to see if the fault returns, ruling out a transient communication glitch

2. 2

   Inspect the wiring harness connecting the Engine ECU to the DEF supply module for chafing, corrosion, or loose pins

3. 3

   Check DEF fluid quality to ensure the tank is free of dirt, diesel, or water contamination

1. 1

   Isolate the Module

   If the wiring harness tests good (continuity and voltage are within spec), the fault lies within the DEF supply module itself.

2. 2

   Replace the DEF Supply Module

   Because the temperature sensor is internal to the DEF supply module (pump) and is not serviceable separately, the entire DEF supply module must be replaced.

3. 3

   Replace Filters

   Replace the DEF supply module filter (cartridge) and inspect the O-rings when installing the new pump to prevent immediate contamination.

4. 4

   System Prime and Clear

   Install the new module, prime the DEF system, and use the WinEEM3s/WinEEM4s Service Tool (or equivalent dealer diagnostic tool) to clear the stored fault codes and reset the emissions derate timer.