Massey Ferguson U 520296 – Engine ECU / Dosing Strategy Monitoring Module: Dosing Strategy Monitoring Module NOx conversion efficiency: Threshold 1 error

The Selective Catalytic Reduction (SCR) system is failing to reduce Nitrogen Oxide (NOx) emissions to the required legal limits. The system calculates this by comparing readings from the upstream and downstream NOx sensors, and the conversion efficiency has dropped below Threshold 1.

• 8670
• 8680
• 8690
• 8727
• 8730
• 8732
• 8735
• 8737
• 8740
• 7714 through 7726
• 6711 through 6718
• 5708 through 5713
• Activa
• BETA

1. 1

   Check the DEF tank for contamination (dirt, diesel, or water dilution) as poor DEF quality is a primary cause of poor NOx conversion

2. 2

   Inspect the DEF pump module, heated supply/return lines, and O-rings for leaks, kinks, or air ingress to ensure correct pressurization

3. 3

   Remove the DEF injector from the exhaust and check for severe urea crystallization or soot blockage preventing proper atomization

4. 4

   Check the wiring harnesses for the NOx sensors, as a failing sensor will often falsely report poor conversion efficiency

1. 1

   Address Fluid Issues

   If the DEF fluid is degraded or contaminated, drain the DEF tank completely, flush it, and replace the DEF filter. Refill with fresh, high-quality 32.5% urea DEF.

2. 2

   Clean/Replace the Doser

   If the DEF dosing module is clogged with crystallized urea, clean the mounting port on the exhaust. If the injector is electrically failed or permanently clogged, replace the dosing module.

3. 3

   Replace the NOx Sensor(s)

   If the fluid and doser are functioning perfectly, the downstream NOx sensor is likely degraded and misreporting the tailpipe emissions. Replace the faulty NOx sensor.

4. 4

   Clear Codes and Test

   Use a heavy-duty agricultural diagnostic tool (such as Texa IDC5, Jaltest Agriculture, or the OEM AGCO EDT) to clear the U 520296 fault code.

5. 5

   Perform SCR System Test

   Run a forced regeneration or an SCR dosing test via the diagnostic tool to verify that the NOx conversion efficiency has returned to normal parameters.