ECU 004366.18 – DEF Tank Heater Coolant Control Valve is Stuck Closed. John Deere System Advisory.

ECU 004366.18 (ECU 4366.18)

Code: 004366.18

Shortcode: 4366.18


This code is triggered when the DEF tank heater coolant control valve is detected to be stuck closed, causing the thawing of the DEF tank to take too long. This can affect the proper heating and operation of the DEF system, potentially leading to DEF freezing and reduced system efficiency.


The ECU may limit or adjust the operation of the DEF system to manage the delayed thawing of the DEF tank, 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 closed. 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 opening.
  • 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.


Ensuring the proper operation of the DEF tank heater coolant control valve is essential for effective DEF injection and system performance, especially in cold conditions. Regular inspections and timely maintenance can prevent valve-related problems.

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