ECU 004334.18 – DEF Dosing Unit Pressure Moderately Low. John Deere System Advisory.

ECU 004334.18 (ECU 4334.18)

Code: 004334.18

Shortcode: 4334.18


This code indicates that the DEF dosing unit pressure is detected to be moderately low. Insufficient pressure can prevent the proper injection of DEF, reducing the effectiveness of the aftertreatment system.


The ECU may limit the operation of the DEF system to prevent potential damage, which can impact overall vehicle performance and emissions compliance.


  • Inspect DEF Dosing Unit and Lines: Check for leaks, blockages, or malfunctions that could cause low pressure in the DEF dosing unit and associated lines. Repair or replace components as necessary.
  • Verify DEF Supply: Ensure that the DEF tank is adequately filled and that there are no blockages in the supply lines.
  • Check Pump Operation: Test the DEF pump to ensure it is operating correctly and providing the necessary pressure.
  • Test Pressure Sensors: Verify that the pressure sensors are providing accurate readings and replace any faulty sensors.
  • Reset ECU and Monitor: After resolving the low pressure issue, reset the ECU to clear the fault code and monitor the system to ensure it maintains the correct pressure.


Proper pressure in the DEF dosing unit is crucial for effective DEF injection and maintaining the efficiency of the aftertreatment system. Regular inspections and maintenance can help prevent low pressure issues.

Control Units: John Deere

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