ECU 004334.00 – DEF Dosing Unit Pressure Extremely High. John Deere System Advisory.

ECU 004334.00 (ECU 4334.00)

Code: 004334.00

Shortcode: 4334.00


This fault code is triggered when the pressure in the Diesel Exhaust Fluid (DEF) dosing unit is detected to be extremely high. Excessively high pressure can damage the dosing unit and impair the proper injection of DEF into the aftertreatment system.


The ECU may issue warnings or limit the operation of the DEF system to prevent damage, potentially affecting the overall efficiency of the emission control system.


  • Inspect DEF Dosing Unit: Check the dosing unit for any blockages or malfunctions that could cause high pressure. Clean or replace components as necessary.
  • Verify Pressure Relief Mechanisms: Ensure that any pressure relief valves or mechanisms in the DEF system are functioning correctly.
  • Check for Contaminants: Inspect the DEF for any contaminants that could be causing clogs and high pressure.
  • Test Pressure Sensors: Verify that the pressure sensors are providing accurate readings and replace them if they are faulty.
  • Reset ECU and Test System: After addressing the high pressure issue, reset the ECU to clear the fault code and test 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.

Control Units: John Deere

John Deere Parts
John Deere Logo