John Deere 4345.05 – ECU: DEF Dosing Unit Supply Line Heater, Resistance Too High

The engine control system monitors the electrical resistance of the heater integrated into the Diesel Exhaust Fluid (DEF) supply line, which prevents the fluid from freezing in cold weather. Fault code 004345.05 indicates that the circuit resistance is too high. This typically points to an open circuit, such as a broken wire in the harness, a disconnected plug, or a burned-out heater element inside the DEF line.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5090M
• 5100M
• 5100MH
• 5100ML
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 8R Series
• 8RW Series
• 8245R
• 8400R
• 9RT Series
• 9470RT
• 9520RT
• 9570RT
• 6105M
• 210G
• 210GLC
• 544K-II
• 4045 PowerTech
• 4.5L OEM Diesel Engine

1. 1

   Initial logic and parameters are validated.

2. 2

   Standard processing applied

3. 3

   Standard processing applied

4. 4

   Turn the key ON and verify that the ECU is sending the proper reference voltage to the heater circuit.

1. 1

   Established context

   Initial logic and parameters are validated.

2. 2

   Standard processing applied

   Standard processing applied

3. 3

   Standard processing applied

   Standard processing applied

4. 4

   Standard processing applied

   Standard processing applied

5. 5

   Standard processing applied

   Standard processing applied

6. 6

   Standard processing applied

   Standard processing applied

7. 7

   Final transformation

   Plug in the heater electrical connector and reconnect the battery.

8. 8

   Clear codes

   Use John Deere Service ADVISOR (or a compatible heavy-duty scan tool) to clear the ECU fault codes. Run the engine to verify the code does not return and check the line fittings for leaks.