ECU 004334.16 – DEF Dosing Unit Pressure Moderately High. John Deere System Advisory.

ECU 004334.16 (ECU 4334.16)

Code: 004334.16

Shortcode: 4334.16


This diagnostic trouble code is set when the DEF dosing unit pressure is detected to be moderately high. Elevated pressure levels can indicate a potential blockage or malfunction within the DEF system that may affect proper DEF dosing.


The ECU may adjust the operation of the DEF system to manage the elevated pressure, potentially impacting DEF injection and overall emissions control efficiency.


  • Inspect DEF Dosing Unit and Lines: Check for blockages or restrictions in the DEF dosing unit and associated lines. Clean or replace components as necessary.
  • Verify 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 cause pressure issues and clean the system if necessary.
  • Test Pressure Sensors: Verify that the pressure sensors are providing accurate readings and replace any faulty sensors.
  • Reset ECU and Monitor System: After addressing the pressure issue, reset the ECU to clear the fault code and monitor the system to ensure normal operation.


Maintaining the correct pressure in the DEF dosing unit is essential for effective DEF injection and proper functioning of the aftertreatment system. Regular maintenance can help prevent pressure-related issues.

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