Massey Ferguson 3516.15 – Engine Control Unit (ECU): DEF Quality Sensor Has Detected A Problem With The DEF Sample.

This code indicates that the Urea Quality Level Sensor (UQLS) has detected that the Diesel Exhaust Fluid (DEF) in the tank is outside the acceptable urea concentration range (which should be 32.5%). This is most commonly caused by fluid contamination (e.g., water, diesel, dirt, or coolant mixed into the DEF), degraded fluid from improper storage, or a malfunctioning quality sensor.

• 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

   Visual Inspection: Check the DEF fluid in the tank. It should be clear. If it appears cloudy, discolored, or contains visible debris, it is contaminated.

2. 2

   Refractometer Test: Extract a sample of the DEF and test it using a DEF refractometer. The urea concentration must be exactly 32.5% (acceptable range is 31.8% - 33.2%).

3. 3

   Temperature Check: DEF freezes at 12°F (-11°C). If operating in cold weather, ensure the tank heater is functioning properly and the fluid is not frozen.

4. 4

   Wiring & Connector Check: Inspect the wiring harness and connector at the top of the DEF tank (where the UQLS is located) for corrosion, chafing, or loose pins.

1. 1

   Do not start the engine

   If severe contamination (like diesel fuel) is suspected, do not start the engine as this will circulate bad fluid and destroy the SCR catalyst and DEF injector.

2. 2

   Drain the DEF tank

   Drain the DEF tank completely.

3. 3

   Flush the tank

   Flush the tank to remove all traces of the contaminant.

4. 4

   Refill the system

   Refill the system with fresh, high-quality, API-certified DEF.

5. 5

   Clear codes and test

   Clear the codes using a diagnostic tool and run the machine to see if the code returns.

6. 6

   Disconnect the battery

   If the fluid tests perfectly at 32.5% but the code remains active (indicating the UQLS has failed internally), disconnect the battery.

7. 7

   Disconnect the electrical harness

   Disconnect the electrical harness from the DEF sensor unit at the top of the DEF tank.

8. 8

   Extract the sensor unit

   Remove the mounting hardware and carefully extract the combined sensor unit from the tank.

9. 9

   Install the new DEF Quality Sensor

   Install the new DEF Quality Sensor, ensuring the O-ring/seal is properly seated to prevent dirt ingress.

10. 10

    Reconnect and clear codes

    Reconnect the harness, refill the tank, and use a diagnostic tool to clear the ECU codes.