John Deere 3517.12 – ECU: DEF Tank Fluid Level Error

The DEF (Diesel Exhaust Fluid) tank fluid level sensor has detected a problem with measuring the fluid level. This typically occurs when the sensor provides inaccurate readings, which can be caused by debris obstructing the sensor's operation, a short circuit/open circuit in the wiring, or a complete failure of the sensor itself. If left unaddressed, the ECU may provide incorrect DEF dosing, leading to reduced effectiveness of the emission control system and eventual engine derate.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5090M
• 5100M
• 5100MH
• 5100ML
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 6105M
• 7210R
• 7310R
• 8245R
• 8400R
• 9R Series
• 9RT Series
• 9RX Series
• 260E
• 310E
• R4023
• W235
• W260
• S-Series

1. 1

   Inspect for Obstructions: Remove the DEF tank level sensor (header assembly) and inspect it for any crystallized DEF, debris, or physical obstructions.

2. 2

   Check the DEF Tank: Inspect the inside of the DEF tank for contaminants that could be blocking the sensor pickup.

3. 3

   Test Wiring and Connections: Check the electrical harness connecting to the DEF header for any signs of a short to a high voltage source or an open circuit.

4. 4

   Test Sensor Functionality: After cleaning any debris, plug the sensor back in and test it to see if it provides accurate fluid level readings to the ECU.

1. 1

   Preparation

   Turn off the machine and ensure the key is removed. Clean the area around the top of the DEF tank to prevent dirt from falling in.

2. 2

   Disconnect

   Unplug the electrical connector from the DEF tank header assembly. Disconnect the DEF pressure and return lines (be prepared for minor fluid spillage).

3. 3

   Removal

   Unbolt or unlatch the DEF tank header assembly from the top of the DEF tank and carefully pull the unit straight up and out.

4. 4

   Clean or Replace

   If cleaning: Thoroughly clean the sensor tube and float area with warm distilled water (do not use harsh chemicals). Clean the tank if necessary. If replacing: Prepare the new DEF tank header assembly.

5. 5

   Reinstallation

   Insert the clean or new header assembly into the tank. Secure the mounting bolts/latches.

6. 6

   Reconnect

   Reattach the DEF fluid lines and plug in the electrical connector.

7. 7

   Reset and Test

   Refill the tank with clean DEF (32.5% urea). Turn the key on, clear the error log/reset the ECU, and monitor the DEF level gauge to ensure accurate reporting.