John Deere 4376.05 – ECU: DEF Dosing Unit Reversing Valve, Resistance Too High

The Engine Control Unit (ECU) sets this code when it detects an open circuit or excessively high resistance in the DEF dosing unit's reversing valve circuit, which prevents the reversing valve from functioning properly and disrupts the DEF dosing process and fluid purge upon shutdown.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5090M
• 5100M
• 5100MH
• 5100ML
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 9RT Series
• 9470RT
• 9520RT
• 9570RT
• 6M Series
• 6105M
• 8RT Series
• S-Series Combines
• X-Series Combines

1. 1

   Inspect wiring and connections for damaged, frayed, or loose wiring in the DEF dosing unit reversing valve circuit

2. 2

   Check the harness connectors at the DEF pump for signs of corrosion or moisture intrusion

3. 3

   Test the reversing valve element at the DEF pump for continuity and proper resistance specifications using a digital multimeter

4. 4

   Verify that the electrical supply voltage to the valve from the ECU is stable and within specifications

1. 1

   Power Down

   Turn off the machine and disconnect the battery power before servicing the DEF system to prevent electrical shorts.

2. 2

   Access the DEF Dosing Unit

   Locate the DEF Dosing Unit (Pump) assembly, typically mounted near the DEF tank.

3. 3

   Repair Wiring/Connectors

   If the diagnostic checks revealed damaged wiring, broken pins, or corrosion, repair the harness or replace the pigtail connector. Clean any mild corrosion with electrical contact cleaner and apply dielectric grease.

4. 4

   Replace the Valve/Pump Assembly

   If the wiring is intact but the reversing valve itself fails the resistance test (open circuit), the valve must be replaced. Note: On most John Deere DEF systems, the reversing valve is integrated internally into the DEF Dosing Unit Pump assembly, so the entire pump must be replaced.

5. 5

   Reassemble and Reconnect

   Install the new DEF pump/valve, reconnect the fluid lines, and plug in the electrical harness. Reconnect battery power.

6. 6

   Reset and Test

   Use a John Deere Service ADVISOR tool (or equivalent diagnostic scanner) to reset the ECU and clear the fault code. Run the engine, allow the aftertreatment system to reach operating temperature, and monitor the system to ensure the code does not return and the DEF system doses and purges correctly.