John Deere 4366.18 – ECU: DEF Tank Insufficient Heating Fault / DEF Tank Heater Coolant Control Valve is Stuck Closed

Triggered when the system detects that the thawing of the Diesel Exhaust Fluid (DEF) tank is taking too long. The engine coolant responsible for thawing the DEF is not flowing properly, typically because the DEF tank heater coolant control valve is stuck in the closed position, or there is a blockage (such as frozen coolant or debris) in the DEF coolant lines.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5090M
• 5100M
• 5100MH
• 5100ML
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 330G
• 331G
• 332G
• 333G
• 260E
• 310E
• 7210R
• 7230R
• 7250R
• 7270R
• 7290R
• 7310R

1. 1

   Inspect DEF coolant lines for frozen or slushy coolant, and ensure engine coolant concentration meets specifications

2. 2

   Check the coolant system for debris (such as casting sand) that may be lodged in the coolant control valve

3. 3

   Inspect wiring and connectors in the coolant valve circuit for damage, fraying, or loose connections

4. 4

   Use a diagnostic tool (e.g., Service ADVISOR) to manually command the DEF Coolant Valve to open and close, listening and feeling for actuation

5. 5

   Measure resistance across the coolant control valve pins at the DEF header connector and compare to expected values for the current tank temperature

1. 1

   Thaw the Machine

   If operating in freezing temperatures, move the machine into a warm shop to allow the DEF and coolant lines to completely thaw.

2. 2

   Attempt to Clean the Valve

   If debris is suspected, attempt to flush the coolant lines and clean the valve.

3. 3

   Replace the Valve / Header

   If the valve is mechanically failed (stuck closed) and cannot be freed, it must be replaced. Note: On many John Deere models (such as the G-Series skid steers), the coolant control valve is integrated directly into the DEF Tank Header Assembly and is not available as a separate serviceable part. In these cases, the entire DEF Header must be replaced.

4. 4

   Reassemble and Refill

   Reconnect all coolant and DEF lines. Top off the engine coolant and DEF fluid levels.

5. 5

   Clear Codes and Test

   Reset the ECU to clear the 004366.18 fault code. Run the machine and monitor the DEF tank temperature via the diagnostic tool to ensure the tank is heating properly and the code does not return.