John Deere 4334.31 – ECU: DEF Dosing Unit Pressure Fault

This diagnostic trouble code is triggered when the DEF dosing unit pressure signal exceeds a threshold value during the suction process. This indicates an anomaly in the DEF urea injection system, typically pointing to an issue with pressure regulation, a blockage, or a defective pressure sensor.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5090M
• 5100M
• 5100MH
• 5100ML
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 9470RT
• 9520RT
• 9570RT
• 8R Series (8245R to 8400R, 8R 340)
• 6105M
• 9500 series
• 9600 series
• 9700 series
• 9800 series
• 210L–710L Backhoes
• 344L Loaders
• 130G Excavators
• 337E/437E Knuckleboom Loaders
• Vermeer D24x40 S3
• Vermeer D40x55

1. 1

   Verify DEF Supply: Ensure the DEF tank is adequately filled and that the fluid is not contaminated or frozen.

2. 2

   Inspect Lines and Hoses: Check all DEF supply and suction lines for leaks, kinks, or blockages that could cause pressure anomalies.

3. 3

   Test Pressure Sensors: Use a diagnostic tool to verify that the pressure sensors on the dosing unit are providing accurate readings.

4. 4

   Perform a Vacuum/Suction Test: Run a DEF Dosing Unit Vacuum Test via the diagnostic software to see if the pump can maintain specification.

5. 5

   Check the DEF Filter: A clogged DEF dosing unit filter is a common cause of pressure faults. Inspect the filter before condemning the pump.

1. 1

   Clean work area

   Clean the area around the DEF dosing unit to prevent dirt from entering the system.

2. 2

   Remove filter cover

   Remove the DEF dosing unit filter cover (A) and discard the equalizing element (B).

3. 3

   Insert filter tool

   Insert the "Black" end of the supplied DEF dosing unit filter tool into the filter until you feel/hear a click, indicating it is fully engaged.

4. 4

   Remove old filter

   Pull the tool and the old filter out of the dosing unit and discard them.

5. 5

   Clean mating surfaces

   Clean the dosing unit threads and mating surfaces with distilled water only. (Note: DEF is highly corrosive. If spilled on painted or unpainted metal, immediately flush the surface with clear water to prevent damage and white residue buildup.)

6. 6

   Lubricate O-rings

   Lubricate the new DEF filter O-rings with clean DEF fluid.

7. 7

   Install new filter

   Carefully insert the new filter, install a new equalizing element, and reinstall the cover.

8. 8

   Reset ECU and test

   Reset the ECU to clear the 004334.31 fault code and run the engine to monitor system pressure. If the pump/sensor assembly has failed internally, the DEF Dosing Unit Pump must be replaced.