Massey Ferguson E4334.03 – Engine Control Unit (ECU): DEF System Pressure Sensor Voltage High (ECU)

The controller is receiving a voltage signal from the Diesel Exhaust Fluid (DEF) pressure sensor that exceeds the normal operating range. This is typically caused by a short circuit to a high voltage source (such as a 12V or 5V supply) or an open circuit in the sensor's wiring harness.

• 7616
• 5612
• 7622
• Interim Tier 4 (2012-2015)
• 7614
• 5611
• 7615
• 5610
• 5613
• 7620
• 5609
• 7618
• 5608
• 7619
• 7626
• 7624
• MF 4707
• MF 4708
• MF 4709
• MF 4710
• MF 5608
• MF 5609
• MF 5610
• MF 5611
• MF 5612
• MF 5613
• MF 5710 SL
• MF 5711 SL
• MF 5712 SL
• MF 5713 SL
• MF 7614
• MF 7615
• MF 7616
• MF 7618
• MF 7619
• MF 7620
• MF 7622
• MF 7624
• MF 7626
• MF 7714
• MF 7715
• MF 7716
• MF 7716S
• MF 7718
• MF 7718S
• MF 7719
• MF 7720
• MF 7720S
• MF 7722
• MF 7722S
• MF 7724
• MF 7724S
• MF 7726
• MF 7726S

1. 1

   Inspect the wiring harness between the Engine ECU and the DEF Supply Module for chafed wires, pinched lines, or exposed copper that could cause a short to a power source.

2. 2

   Disconnect the DEF pump module connector and check for moisture, corrosion, or bent pins (specifically the 5V supply, signal, and ground pins).

3. 3

   Using a multimeter, verify the 5V reference supply and ground at the sensor connector.

4. 4

   Test the signal wire for continuity back to the ECU and ensure it is not shorted to the 5V or 12V lines.

5. 5

   If the wiring harness tests perfectly and the ECU is outputting the correct reference voltage, conclude that the internal DEF pressure sensor has failed.

1. 1

   Turn off the tractor, remove the key, and disconnect the negative battery cable.

2. 2

   Locate the DEF Supply Module.

   Usually mounted near the DEF tank.

3. 3

   Thoroughly clean the area around the module.

   Prevents dirt from entering the SCR system.

4. 4

   Disconnect the main electrical harness from the DEF module.

5. 5

   Relieve any residual pressure and carefully disconnect the DEF suction, backflow, and pressure lines.

   Cap the lines immediately to prevent crystallization and contamination.

6. 6

   Unbolt the mounting hardware and remove the faulty DEF Supply Module.

7. 7

   Install the new DEF Supply Module and torque the mounting bolts to OEM spec.

8. 8

   Reconnect the DEF fluid lines.

   Ensure they click securely into place.

9. 9

   Reconnect the electrical harness and the battery.

10. 10

    Connect a diagnostic service tool to clear the E4334.03 / SPN 4334 fault code.

    Use a tool like AGCO EDT or Bosch ESI[truck].

11. 11

    Run an SCR system test or start the engine to build DEF pressure.

    Verify there are no leaks and the code does not return.