John Deere 3516.12 – ECU: Aftertreatment DEF Concentration Sensor Error

The DEF (Diesel Exhaust Fluid) concentration sensor has detected a malfunction within its system, impacting its ability to accurately measure the DEF concentration. This code is triggered by a hardware failure of the sensor itself, incorrect sensor calibration, or an electrical circuit issue affecting the sensor's operation.

• 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
• 8245R to 8400R
• 8RT 370
• 9470RT
• 9520RT
• 9570RT
• 710P
• 710L
• 544K
• R4023
• W235
• W260

1. 1

   Test the DEF Fluid: Verify the DEF fluid quality using a refractometer. It should measure exactly 32.5% urea and 67.5% deionized water.

2. 2

   Inspect the Wiring Harness: Check the electrical connector at the DEF tank header for corrosion, bent pins, or water intrusion. Inspect the wiring harness leading back to the ECU for chafing or short circuits.

3. 3

   Check for Accompanying Codes: Look for related codes like 3516.14 (DEF Contaminated) or 3516.16 (DEF Concentration Moderately High). If 3516.12 is the only code, the sensor itself is the most likely culprit.

4. 4

   Monitor Live Data: Use John Deere Service ADVISOR or a compatible diagnostic tool to monitor the live data from the DEF quality sensor to see if the readings are erratic, frozen, or completely out of range.

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 falling into the tank.

2. 2

   Drain Fluid

   If there is any suspicion of contamination, drain the DEF tank completely.

3. 3

   Disconnect Lines

   Carefully disconnect the DEF supply and return lines from the top of the DEF tank header.

4. 4

   Disconnect Electrical

   Unplug the electrical harness connector from the header.

5. 5

   Remove the Header

   Unscrew the retaining ring or unbolt the fasteners holding the DEF tank header assembly to the tank. Carefully pull the long header assembly straight up and out of the tank.

6. 6

   Install the New Part

   Insert the new DEF tank header assembly into the tank, ensuring the O-ring/gasket is properly seated to prevent leaks. Secure the retaining ring or bolts.

7. 7

   Reconnect

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

8. 8

   Refill

   Refill the tank with fresh, certified DEF.

9. 9

   Clear Codes

   Reconnect the battery, connect a diagnostic tool, and clear the ECU 003516.12 fault code. Run the engine to verify the code does not return and that the ECU is reading the new sensor correctly.