Massey Ferguson 3521.31 – Engine ECU: DEF Quality Sensor Has Detected A Problem With The DEF Sample

The DEF quality sensor has measured the urea concentration in the DEF tank and found it to be outside the required specification (which must be a precise 32.5% urea solution in de-ionized water). This code is triggered by fluid contamination, degraded fluid, or a mechanical/electrical failure of the sensor itself.

• 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
• 4700 Series
• 5600 Series
• 5608
• 5609
• 5610
• 5611
• 5612
• 5613
• 5700SL Series
• 7600 Series
• 7614
• 7626
• 7700 Series
• 7700S Series
• 8700 S Series

1. 1

   Test the DEF concentration using a DEF refractometer directly from the tank (should read exactly 32.5%).

2. 2

   Visually inspect the DEF tank, filler neck, cap, and breather for dirt, dust, or signs of diesel fuel/water mixed into the DEF.

3. 3

   Inspect the wiring harness and connector going to the DEF quality sensor on the tank unit for corrosion, chafing, or loose pins.

1. 1

   Drain the Tank

   Completely dump/drain the DEF tank to remove the contaminated or degraded fluid.

2. 2

   Clean the Tank

   Flush the tank to ensure no residual dirt, diesel, or crystallized urea remains. Ensure the tank neck and cap are spotless.

3. 3

   Replace the Sensor

   If the fluid tested fine but the code persists, or if the sensor is physically damaged/crystallized beyond cleaning, remove the old DEF quality sensor assembly from the tank and install the new OEM sensor.

4. 4

   Refill

   Refill the tank with fresh, clean, in-date DEF (AdBlue) from a sealed container.

5. 5

   Clear Codes

   Use a compatible diagnostic tool (such as AGCO EDT or Jaltest AGV) to clear the 003521.31 fault code from the Engine ECU.

6. 6

   Test Run

   Run the tractor to allow the system to pressurize, sample the new fluid, and verify that the code does not return.