John Deere 4334.16 – Engine Control Unit (ECU): DEF Dosing Unit Pressure Moderately High

The Engine Control Unit (ECU) has detected a high voltage signal from the DEF System Pressure Sensor, indicating that the DEF dosing unit pressure is moderately high. This fault can be triggered by an electrical issue, such as an open circuit or a voltage-above-normal condition in the sensor's wiring, or by a genuine high-pressure condition within the DEF system caused by blockages or pump malfunctions.

• 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
• 8245R through 8400R
• 6105M
• 5085M
• 5095M
• 5105M
• Vermeer D24x40 S3
• Vermeer D40x55 S3

1. 1

   Inspect the DEF dosing unit and all associated lines for physical blockages, kinks, or malfunctions that could prevent pressure relief

2. 2

   Ensure that the pressure relief mechanism/valve inside the DEF dosing unit is functioning correctly

3. 3

   Inspect the DEF fluid for dirt, debris, or crystallization that could be causing pressure blockages

4. 4

   Use a diagnostic tool to monitor the DEF pressure sensor live data to ensure it is providing accurate readings and not defaulting to a falsely high value

1. 1

   Preparation

   Turn off the machine, disconnect the batteries, and allow the aftertreatment system to cool and depressurize.

2. 2

   Clear Blockages

   If any DEF lines were found to be kinked or blocked during diagnosis, clean or replace the affected lines.

3. 3

   Address Contamination

   If the DEF fluid is contaminated, drain the DEF tank, flush the system, replace the DEF pump filter, and refill with fresh, high-quality Diesel Exhaust Fluid.

4. 4

   Replace Faulty Sensor

   If diagnostic testing proved the DEF pressure sensor is reading falsely high, replace the sensor.

5. 5

   Replace DEF Dosing Unit

   If the lines are clear, the sensor is accurate, and the unit still fails to relieve pressure internally during shut-off/suction sequences, the internal pressure relief mechanism has failed. You will need to replace the DEF Dosing Unit Pump assembly.

6. 6

   Reassembly and Reset

   Reconnect the batteries. Use a diagnostic tool to reset the ECU and clear the 004334.16 fault code.

7. 7

   Validation

   Run the machine through a standard operating cycle and monitor the DEF system pressure to ensure normal operation and verify the code does not return.