John Deere 5745.31 – ECU: DEF Dosing Unit Heater, Temperature Faulty or DEF Supply Module Fault

The Engine Control Unit has detected that the DEF dosing unit heater on-time is faulty, or the temperature reading from the DEF supply module is invalid/moderately low. This is frequently triggered by a physical failure where DEF leaks internally and enters the electrical connector, or unintentionally by outdated engine software.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5090M
• 5100M
• 5100MH
• 5100ML
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 6M Series (6105M, 6130M-6230M)
• 6R Series (6110R-6250R)
• 7R Series (7210R-7310R)
• 8R/8RT Series (8245R-8400R)
• 9RT Series (9470RT, 9520RT, 9570RT)
• 310L
• 310SL
• 315SL
• 130G
• 344L
• 437E
• 337E

1. 1

   Check for Software Updates: Verify the ECU software is up to date before replacing hardware to prevent unintentional setting of DEF Supply Module Temperature Fault (5745.31 DTC).

2. 2

   Inspect the Electrical Connector: Disconnect the wiring harness at the DEF Dosing Unit/Supply Pump and inspect the pins and the connector body for liquid DEF intrusion or crystallization.

3. 3

   Check for Cascading Codes: Look for accompanying codes such as ECU 5435.31 (DEF Pressure Low) or ECU 157.04.

1. 1

   Proper Shutdown

   Turn off the machine and wait for the DEF system to complete its purge cycle.

2. 2

   Disconnect Power

   Disconnect the machine's battery completely.

3. 3

   Clean the Harness

   If DEF fluid is found in the wiring harness connector during the diagnostic check, thoroughly clean the electrical connector on the machine side using an appropriate electronic contact cleaner to remove all DEF residue.

4. 4

   Replace the Pump

   Remove the faulty DEF Dosing Unit Pump assembly and install the replacement unit.

5. 5

   Reconnect and Clear

   Reconnect the battery, turn on the machine, and use a diagnostic tool to clear the ECU 5745.31 fault code.