Massey Ferguson 3516.02 – Engine Control Unit (ECU): DEF Quality Sensor Has Detected A Low Quality DEF Sample.

The system has detected that the Diesel Exhaust Fluid (DEF / AdBlue) in the tank does not meet the required 32.5% urea concentration. This can be caused by contaminated fluid (e.g., water, dirt, or diesel mixed in), degraded fluid from extreme temperatures, crystallization on the sensor, or a physical failure of the DEF quality sensor itself. If left unresolved, the machine will enter a "derate" mode, significantly reducing engine power.

• 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
• 5710 SL
• 5711 SL
• 5712 SL
• 5713 SL
• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626

1. 1

   Test the DEF in the tank using a DEF refractometer to ensure it is exactly 32.5% urea. Check for signs of water dilution, diesel fuel contamination, or dirt.

2. 2

   Inspect the DEF tank filler neck and cap. A damaged cap or breather can allow moisture and dust to enter.

3. 3

   Check the wiring loom, connectors, and terminals leading to the DEF quality sensor for corrosion, loose contacts, or chafing.

4. 4

   Look for white urea crystals around the sensor or inside the tank, which can block the sensor from reading accurately.

1. 1

   Drain and Flush

   If the DEF is contaminated, degraded, or crystallized, completely drain the DEF tank. Flush the tank to remove any residual impurities.

2. 2

   Refill

   Refill the tank with fresh, high-quality, in-date DEF (AdBlue).

3. 3

   Clear Codes & Test

   Use a diagnostic scanner (such as the AGCO Electronic Diagnostic Tool) to clear the fault codes. Perform a key cycle, start the engine, and let it idle to validate if the sensor reads the new fluid correctly.

4. 4

   Replace Sensor

   If the code returns immediately or the sensor is physically damaged/shorted, the DEF Quality Sensor (often integrated into the tank sender unit) must be replaced.

5. 5

   Final Validation

   After installing the new sensor, clear the codes again and run the engine to ensure the derate is lifted and the ECU registers the correct DEF concentration.