John Deere 3516.16 – Engine Control Unit (ECU): Aftertreatment DEF Concentration Moderately High

The DEF quality/concentration sensor has detected that the urea concentration in the DEF tank is moderately higher than the required specification, or that an incorrect/contaminated fluid is present. This condition disrupts the chemical reactions needed for the Selective Catalytic Reduction (SCR) system to reduce emissions, which will typically prompt the machine to enter a derate mode to prevent damage.

• 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
• 7210R
• 7230R
• 7250R
• 9470RT
• 9520RT
• 9570RT
• R4023
• W235
• W260
• 710 P
• 710L

1. 1

   Verify DEF Fluid Quality: Use a refractometer to test the DEF concentration in the tank. Standard ISO 22241-certified DEF should measure at approximately 32.5% urea and 67.5% deionized water.

2. 2

   Inspect for Contamination: Check the DEF tank for dirt, water, or the accidental addition of other fluids (like diesel or coolant).

3. 3

   Inspect the DEF Sensor: Check the DEF concentration sensor (located on the DEF header assembly inside the tank) for physical damage, corrosion, or crystallization.

4. 4

   Check for Software Updates: For certain models (like the 7R Tier 4 Series), John Deere released engine software updates (e.g., SW63631B / SW63225B) specifically to update SCR derate handling in cases of high DEF concentration (DTC 3516.16). Check if the ECU requires a flash update.

1. 1

   Drain the DEF Tank

   If the refractometer confirms the DEF concentration is incorrect or contaminated, completely drain the DEF tank.

2. 2

   Flush the System

   Clean and flush the aftertreatment pickup and delivery system to remove any residual contaminated fluid that could damage the dosing injector or SCR catalyst.

3. 3

   Clean or Replace the Sensor

   If the DEF quality sensor is heavily corroded or fails to read correctly after cleaning, replace the DEF Tank Header Assembly (the quality sensor is typically integrated into this unit).

4. 4

   Refill the Tank

   Refill the DEF tank with fresh, high-quality, ISO 22241-certified DEF.

5. 5

   Reset and Test

   Reset the ECU using a diagnostic tool to clear the fault code. Run the machine and perform an emission test or forced regeneration cycle to ensure the aftertreatment system is operating correctly and the code does not return.