John Deere 5745.05 – ECU: DEF Dosing Unit Heater, Resistance Too High

This diagnostic trouble code indicates that the circuit resistance for the Diesel Exhaust Fluid (DEF) dosing unit heater is too high. This condition typically points to an open circuit—meaning there is a break in the wiring, a disconnected plug, or a failed internal heater element.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5090M
• 5100M
• 5100MH
• 5100ML
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 9470RT
• 9520RT
• 9570RT
• 8245R to 8400R
• 6105M
• 5075GV
• 5090GV
• 5075GN
• 5090GN
• 5100GN
• 5075GL
• Vermeer D24x40 S3
• Vermeer D40x55 S3
• Hitachi/Deere 670G

1. 1

   Inspect Wiring and Connections: Visually inspect the wiring harness and connectors leading to the DEF dosing unit/supply module. Look for damaged, frayed, or loose wiring, as well as backed-out pins or corrosion inside the connector.

2. 2

   Check for Open Circuits: Trace the circuit from the ECU to the DEF dosing unit to check for any breaks or discontinuities that would cause high resistance.

3. 3

   Test the DEF Dosing Unit Heater: Disconnect the DEF dosing unit heater and use a digital multimeter to test the heater element for proper resistance and continuity. If the multimeter reads infinite resistance (OL), the internal heater element is broken.

4. 4

   Verify Electrical Supply: Ensure that the electrical supply (including relays and fuses, such as the DEF Supply Module Heater Power fuse) is stable and within specifications.

1. 1

   Safety First

   Turn off the machine, remove the key, and disconnect the battery to ensure safety and prevent electrical shorts.

2. 2

   Locate the Component

   Locate the DEF Dosing Unit / Supply Module (typically mounted near the DEF tank or integrated into the SCR system framework).

3. 3

   Harness Repair

   If your diagnostic checks revealed a broken wire or corroded connector, repair the wiring harness or replace the pigtail connector.

4. 4

   Replace the Heater/Module

   If the wiring is intact but the heater element failed the continuity test, the heater must be replaced. On most John Deere Tier 4 systems, the heater is integrated into the DEF Supply Module / Dosing Unit Pump, requiring replacement of the entire module.

5. 5

   Installation

   Install the new DEF Supply Module. Reconnect all DEF fluid lines and electrical connectors securely.

6. 6

   Reassemble and Reconnect

   Reconnect the battery.

7. 7

   Clear Codes

   Turn the ignition key to the ON position. Use a diagnostic tool (such as John Deere Service ADVISOR or a compatible scanner like TEXA) to clear the ECU fault codes.

8. 8

   Test Operation

   Start the engine and monitor the system to ensure the fault code does not return and the DEF system operates normally.