John Deere 4366.05 – ECU: DEF Tank Heater Coolant Control Valve Circuit Has High Resistance

This condition indicates an open circuit in the DEF tank heater coolant valve circuit. Because the resistance is too high, the coolant valve cannot function properly, which prevents the system from adequately heating and thawing the Diesel Exhaust Fluid (DEF) tank in cold conditions.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5090M
• 5100M
• 5100MH
• 5100ML
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 331G
• 333G
• 330G
• 332G
• 260E
• 310E
• 6105M
• Vermeer D24x40 S3
• Vermeer D40x55 S3

1. 1

   Visually inspect the DEF tank heater coolant valve circuit for damaged, frayed, or loose wiring and connectors

2. 2

   Inspect the electrical contacts at the valve and harness for signs of corrosion, which is a primary cause of high resistance

3. 3

   Use a multimeter to test the coolant valve element for continuity and proper resistance at the DEF header connector (typically between pins 4 and 5)

4. 4

   Ensure that the electrical supply to the valve is stable and that there are no breaks (open circuits) in the harness leading back to the ECU/DCU

1. 1

   Relieve Pressure

   Before disconnecting any coolant lines, ensure the engine is cool and relieve pressure in the cooling system to prevent injury.

2. 2

   Repair Wiring

   If the diagnostic checks reveal frayed wires or corroded connectors, repair or replace the affected section of the wiring harness.

3. 3

   Replace the Valve/Header

   If the wiring is intact but the valve fails the resistance test, the DEF tank heater coolant control valve must be replaced. Note: On many John Deere applications, the coolant control valve is integrated directly into the DEF Tank Header assembly and is not serviceable separately. In this case, the entire DEF header must be replaced.

4. 4

   Reassemble and Refill

   Reconnect all electrical connectors and coolant lines. Refill and bleed the engine coolant system if any fluid was lost during the swap.

5. 5

   Reset and Monitor

   Reset the ECU using a diagnostic tool to clear the 004366.05 fault code. Run the machine and monitor the DEF system to ensure the coolant valve operates correctly and the code does not return.