John Deere 3031.12 – Engine Control Unit (ECU): DEF Tank Fluid Temperature Error

The system has detected that the temperature sensor for the Diesel Exhaust Fluid (DEF) tank is providing an implausible reading, an abnormal rate of change, or is failing to communicate properly, which typically triggers an emissions-related engine derate (inducement).

• 5085E
• 5090E
• 5090EL
• 5100E
• 5090M
• 5100M
• 5100MH
• 5100ML
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 331G
• 333G
• 260E
• 310E
• 5M Series
• 6M Series
• 6105M
• 6R Series
• 7R Series
• 8R Series
• 8RT Series
• 8RX Series
• 8245R
• 8400R
• S-Series
• W-Series
• T-Series
• R-Series
• R4030
• R4038

1. 1

   Visual Inspection: Inspect the DEF tank header assembly, the temperature sensor wiring, and the main engine harnesses (e.g., Rear Engine Harness W1 or Left Main Harness W3) for signs of physical damage, corrosion, or loose connections.

2. 2

   Voltage Testing: Measure the voltage at the temperature sensor to confirm it matches expected specifications. Look for a short to ground or a short to a 12V power source.

3. 3

   Check for Accompanying Codes: Look for related codes such as 003031.03 (Voltage Too High), 003031.04 (Voltage Too Low), or 004366.16 (DEF Tank Temperature Moderately High), which can help pinpoint if the issue is a short circuit or a heating system failure.

4. 4

   Live Data Verification: Use a diagnostic tool (like John Deere Service ADVISOR) to monitor the live DEF temperature reading. If the reading is completely implausible (e.g., showing extreme negative or positive temperatures when ambient is normal), the sensor itself has likely failed.

5. 5

   Software Check: Verify if the ECU software is up to date, as software malfunctions can sometimes trigger false implausibility codes.

1. 1

   Preparation

   Turn off the machine, disconnect the battery, and thoroughly clean the area around the top of the DEF tank to prevent dirt from contaminating the DEF system.

2. 2

   Drain the DEF Tank

   Drain the Diesel Exhaust Fluid from the tank into a clean container (if reusing) or dispose of it properly.

3. 3

   Disconnect Lines and Wiring

   Carefully disconnect the electrical wiring harness connector from the DEF tank header. Disconnect the DEF supply, return, and coolant/heating lines from the header. Cap all lines immediately to prevent contamination.

4. 4

   Remove the Header

   Unbolt or unlatch the locking ring securing the DEF tank header assembly to the top of the DEF tank. Carefully pull the header assembly out of the tank.

5. 5

   Install New Header

   Insert the new DEF tank header assembly (or sensor kit) into the tank, ensuring the O-ring or gasket is properly seated. Secure the locking ring or bolts.

6. 6

   Reconnect

   Reconnect all DEF fluid lines, coolant lines, and the electrical harness.

7. 7

   Refill

   Refill the tank with high-quality, uncontaminated DEF.

8. 8

   Clear Codes and Reset

   Reconnect the battery. Use a diagnostic tool to clear the 003031.12 fault code from the ECU. Because this fault causes an emissions inducement (engine derate), you must perform an "Inducement Unlock" or "Counter Reset" via the diagnostic tool to restore full engine power.