Case IH F-3516-31 - ECU – Engine Control Unit (ECU): DEF/AdBlue concentration is out of range

Triggers when the Urea Quality Sensor (UQS) detects that the Diesel Exhaust Fluid (DEF) concentration has fallen outside the acceptable operating range (approximately 32.5% urea). This is typically caused by DEF that has been diluted with water, degraded from age or extreme heat exposure, or by an internal failure of the DEF quality sensor itself.

• MAGNUM AFS Connect
• Maxxum (115-150)
• Puma (150-220)
• Magnum (180-380)
• Optum
• Steiger (370-620)
• Farmall series
• Various Case IH combines
• Case CE equipment

1. 1

   Test the DEF fluid currently in the tank using a DEF refractometer (must read exactly 32.5% urea concentration)

2. 2

   Inspect the DEF tank for signs of water dilution, diesel fuel contamination, or crystallization

3. 3

   Check the wiring harness and connector leading to the DEF Head Unit / Urea Quality Sensor for corrosion, chafing, or loose pins

4. 4

   Look for other active codes related to DEF temperature or tank level (multiple simultaneous sensor failures indicate the entire DEF Head Unit has likely failed)

1. 1

   Drain the Tank

   If the DEF tests out of range or is of unknown age, completely drain the DEF tank.

2. 2

   Replace the Filter

   Remove and replace the DEF supply filter, as degraded fluid often clogs the filter media.

3. 3

   Refill

   Flush the tank and refill it with fresh, high-quality DEF (32.5% urea).

4. 4

   Clear and Retest

   Clear the fault codes using a diagnostic tool and run the machine through a standard operating cycle or forced regeneration to see if the code returns.

5. 5

   Replace the Sensor/Header

   If the code persists after fresh fluid has been introduced and circulated, the DEF Quality Sensor (which is usually integrated into the DEF Head Unit) has failed internally and must be replaced.