Massey Ferguson 4375.05 – Engine Control Unit (ECU): DEF Pump Control Issue (ECU)

This code indicates an issue with the DEF (Diesel Exhaust Fluid) pump motor control signal. Specifically, the FMI 05 extension in standard J1939 protocol designates "Current Below Normal or Open Circuit." The Engine Control Unit is detecting an open circuit or abnormally low amperage on the control circuit that drives the DEF pump motor.

• 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

   Trace the wiring harness from the Engine ECU to the DEF pump module, looking for chafed wires, rodent damage, or broken lines

2. 2

   Disconnect the DEF pump connector and the ECU connector to inspect for pushed-back pins, corrosion, or water ingress (DEF fluid crystallization)

3. 3

   Use a multimeter to check the continuity of the control and ground wires between the ECU and the DEF pump

4. 4

   Measure the internal resistance of the DEF pump motor at the pump connector to check for an internal failure (infinite resistance indicates a completely open circuit)

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the battery to prevent shorting the ECU during repair.

2. 2

   Repair Wiring

   If the diagnostic tests revealed a broken wire or corroded connector, repair the harness using OEM-approved weatherproof splices and dielectric grease.

3. 3

   Replace the DEF Pump

   Drain the DEF tank or clamp the supply lines to prevent fluid loss. Disconnect the electrical harness and the DEF fluid lines (supply, return, and dosing lines) from the pump module. Unbolt the DEF pump from its mounting bracket. Install the new DEF pump module and reconnect the fluid lines, ensuring the O-rings are seated properly to prevent leaks. Reconnect the electrical harness.

4. 4

   Prime and Test

   Reconnect the battery. Turn the key to the ON position to allow the system to prime. Use a diagnostic scan tool to clear the 004375.05 fault code and run a forced DEF dosing test or SCR system test to verify the pump is building pressure and operating within normal amperage parameters.