Massey Ferguson 3516.11 – Engine Control Unit (ECU): DEF Quality Sensor Has Detected A Problem With Something Covering The Sensor.

The DEF Quality Sensor (submerged in the DEF tank to measure the 32.5% urea concentration and fluid temperature) is unable to take an accurate reading. The system has detected that the sensor element is physically obstructed by crystallized DEF, sludge, dirt, or foreign debris.

• 4710
• 7724S
• 5712SL
• 7722S
• 7722
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 4708
• 7726S
• 4707
• 4709
• 5711SL
• 7718S
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 7720
• Tier 4 (2015-2021)
• 7715S
• 7724
• 5608
• 5609
• 5610
• 5611
• 5612
• 5613
• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626

1. 1

   Inspect the DEF tank filler neck, cap, and breather for dirt, diesel fuel, or water ingress (leading causes of sensor fouling).

2. 2

   Test the DEF fluid using a refractometer to ensure it is exactly 32.5% urea, as contaminated fluid causes sludge.

3. 3

   Remove the DEF header/sensor unit from the tank and visually inspect the probe for heavy white crystallization or debris physically blocking the sensor element.

4. 4

   Inspect the wiring harness and connector at the DEF header for corrosion, bent pins, or damage causing a false reading.

1. 1

   Preparation

   Turn off the tractor, disconnect the battery, and clean the area around the top of the DEF tank to prevent dirt from falling in.

2. 2

   Disconnect the Header

   Disconnect the electrical connector and the heated DEF supply/return lines from the DEF header unit.

3. 3

   Remove the Sensor

   Carefully unscrew the locking ring or mounting bolts and pull the DEF sensor/header assembly out of the tank.

4. 4

   Clean the Sensor (If Applicable)

   If the sensor is covered in crystallized urea, gently clean the probe using warm distilled water. Do not use harsh chemicals, brake cleaner, or abrasives, as this will permanently damage the ultrasonic sensor.

5. 5

   Address Tank Contamination

   If the tank contains sludge or debris, drain the DEF completely and flush the tank with distilled water before reinstalling any parts.

6. 6

   Replace the Sensor

   If cleaning does not resolve the issue or the sensor is permanently failed, install a new DEF sensor unit. Ensure the O-ring is seated correctly to prevent leaks.

7. 7

   Reassembly

   Reconnect the DEF lines and electrical connector. Refill the tank with fresh, high-quality DEF.

8. 8

   Clear Codes

   Reconnect the battery. Use a diagnostic scan tool to navigate to the "Clear Codes" or "Reset Codes" menu and clear 003516.11 from the ECU.

9. 9

   Verification

   Run the tractor to monitor performance and verify that the code does not return and the engine does not enter a derate condition.