Massey Ferguson 4375.03 – Engine Control Unit (ECU) / EEM4: DEF Pump Control Issue / DEF pump motor control signal short circuit to HIGH SOURCE

The engine management system has detected that the control signal circuit for the Diesel Exhaust Fluid (DEF) pump motor is shorted to a high voltage source (battery voltage). This prevents the DEF pump from operating correctly, halting the injection of DEF into the SCR (Selective Catalytic Reduction) system.

• 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
• 5710 SL
• 5711 SL
• 5712 SL
• 5713 SL

1. 1

   Inspect the wiring harness running from the Engine ECU to the DEF pump (Denoxtronic supply module) for chafed wires, melted insulation, or areas where the harness may be rubbing against a power source.

2. 2

   Disconnect the DEF pump connector and the ECU connector. Inspect for water ingress, corrosion, or bent pins that could be bridging the control signal pin to a power pin.

3. 3

   With the DEF pump and ECU disconnected, turn the ignition ON. Use a multimeter to measure the voltage on the DEF pump motor control signal wire. If 12V/24V is present, the wiring harness is shorted to a high source.

4. 4

   If the harness tests good, check for an internal short circuit to high source within the DEF pump motor itself or, less commonly, an internal failure of the ECU's powerstage.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the machine's battery to prevent electrical spikes.

2. 2

   Isolate the Fault

   Based on the diagnostic checks, determine if the fault lies in the wiring harness or the DEF pump module.

3. 3

   Repair Wiring (If Applicable)

   If a short to power was found in the harness, locate the chafed section, repair the wire using OEM-approved heat-shrink connectors, and re-loom the harness away from heat sources or sharp edges.

4. 4

   Replace DEF Pump (If Applicable)

   If the harness is intact and the pump is internally shorted: Relieve any residual pressure in the DEF lines. Disconnect the DEF supply and return lines from the pump module. Disconnect the electrical harness. Unbolt the DEF pump module from its mounting bracket and remove it. Install the new DEF pump module, reconnect the fluid lines, and plug in the electrical connector.

5. 5

   Clear Codes and Test

   Reconnect the battery. Use the WinEEM3/WinEEM4 service tool (or a compatible diagnostic scanner) to clear the 004375.03 / SPN 4375 FMI 3 fault code. Run the engine and perform a forced DEF system test or dosing test to verify the pump motor operates without throwing the code.