ECU 004366.16 – DEF Tank Heater Coolant Control Valve is Stuck Open. John Deere System Advisory.

ECU 004366.16 (ECU 4366.16)

Code: 004366.16

Shortcode: 4366.16


This diagnostic trouble code indicates that the DEF tank heater coolant control valve is stuck open, leading to a DEF tank temperature that is higher than expected. This can affect the proper heating and operation of the DEF system, potentially causing performance issues.


The ECU may limit or adjust the operation of the DEF system to manage the high DEF tank temperature, potentially impacting DEF injection and overall emissions control efficiency.


  • Inspect Control Valve: Check the DEF tank heater coolant control valve for any mechanical issues that might cause it to remain open. Clean or replace the valve if necessary.
  • Inspect Wiring and Connections: Check for damaged, frayed, or loose wiring and connectors in the coolant valve circuit. Repair or replace as necessary.
  • Test Valve Operation: Use diagnostic tools to test the operation of the coolant control valve. Ensure it can open and close as required.
  • Check for Obstructions: Inspect the valve and associated components for any obstructions that might prevent the valve from closing.
  • Reset ECU and Monitor System: After addressing the issue, reset the ECU to clear the fault code and monitor the system to ensure the valve operates correctly.


Proper operation of the DEF tank heater coolant control valve is crucial for maintaining the correct DEF tank temperature and ensuring effective DEF injection. Regular maintenance can help prevent valve-related issues.

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