John Deere 5435.11 – Engine Control Unit (ECU): DEF Dosing Unit Pump Circuit Fault / DEF Dosing Unit Failed to Prime

The DEF dosing unit pump motor is unable to build pressure when priming. This indicates a failure in the pump circuit or an inability of the pump to draw fluid and pressurize the Diesel Exhaust Fluid (DEF) system for injection.

• 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/RW Series (8245R to 8400R)
• 6105M
• 350G LC
• Vermeer D24x40 S3
• Vermeer D40x55 S3

1. 1

   Inspect Wiring and Connections: Check for damaged, frayed, or loose wiring associated with the CAN bus between the ECU and the DEF dosing unit.

2. 2

   Check for Corrosion: Verify that all electrical connections at the DEF dosing unit and the ECU are secure and free of corrosion.

3. 3

   Test CAN Bus Communication: Use a diagnostic tool to test the communication between the ECU and the DEF dosing unit to ensure there are no data transfer interruptions.

4. 4

   Inspect DEF Supply: Ensure the DEF tank has adequate fluid and that the suction lines are not blocked, kinked, or leaking air, which would prevent the pump from priming.

5. 5

   Check DEF Pump Filter: A clogged DEF pump filter can prevent the system from building pressure.

1. 1

   Resolve Wiring Issues

   Repair or replace any damaged CAN bus wiring or corroded connectors found during the diagnostic phase.

2. 2

   Service the DEF Filter

   If the pump is struggling to prime due to a restriction, replace the DEF injection pump filter.

3. 3

   Replace the DEF Dosing Unit Pump

   If wiring is intact, the filter is clean, and the pump still fails to prime or build pressure, the DEF Dosing Unit Pump itself has failed and must be replaced.

4. 4

   Reset and Monitor

   After replacing the pump or repairing the circuit, use a diagnostic tool to reset the ECU, clear the fault code, and run the machine to monitor the system and ensure normal DEF dosing operation.