ECU 004334.31 – DEF Dosing Unit Pressure Fault. John Deere System Advisory.

ECU 004334.31 (ECU 4334.31)

Code: 004334.31

Shortcode: 4334.31


This diagnostic trouble code is triggered when the DEF dosing unit pressure signal exceeds a threshold value during the suction process. This condition indicates that there may be an issue with the pressure regulation or sensor accuracy.


The ECU may limit or adjust DEF system operation to manage the detected pressure fault, potentially impacting DEF injection and overall emissions control.


  • Inspect DEF Dosing Unit: Check the DEF dosing unit for any malfunctions or blockages that could cause pressure irregularities. Clean or replace components as necessary.
  • Test Pressure Relief Mechanism: Ensure that the pressure relief valves or mechanisms are functioning correctly.
  • Check for Contaminants: Inspect the DEF for any contaminants that could be causing pressure issues and clean the system if necessary.
  • Verify Pressure Sensors: Use diagnostic tools to test the pressure sensors and ensure they are providing accurate readings. Replace any faulty sensors.
  • Reset ECU and Monitor System: After addressing the pressure fault, reset the ECU to clear the fault code and monitor the system to ensure normal operation.


Maintaining accurate pressure regulation in the DEF dosing unit is essential for effective DEF injection and proper functioning of the aftertreatment system. Regular inspections and timely repairs can help prevent pressure-related faults.

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