Massey Ferguson U 520260 – Engine ECU / SCR Control Unit: Urea pressure buildup: Pressure buildup failed

The Selective Catalytic Reduction (SCR) system is unable to pressurize the Diesel Exhaust Fluid (DEF / AdBlue) to the commanded level required for injection into the exhaust stream.

• 8600 Series
• 8650
• 8660
• 8670
• 8680
• 8690
• 7700 Series
• 6700 S Series
• 7600 Series

1. 1

   Verify the DEF/AdBlue tank has adequate fluid and check for any contamination (dirt, diesel, or water).

2. 2

   Inspect the heated DEF supply and return lines for kinks, rub points, or damaged O-rings and quick connectors.

3. 3

   Ensure the DEF tank cap and breather are sound to prevent vacuum locks, dust, and moisture ingress.

4. 4

   Inspect the fine filter/strainer inside the DEF pump/head module for blockages or crystallization.

5. 5

   Check the urea pressure sensor and wiring harness for damage, verify the power supply circuit, and check for shorts or open circuits.

1. 1

   Clean the Area

   Before opening any part of the DEF system, thoroughly clean the tank neck and pump area to prevent dirt from entering the system.

2. 2

   Resolve Line Restrictions

   If any heated DEF lines are kinked, leaking, or have damaged O-rings, replace the affected lines or seals to ensure an airtight circuit.

3. 3

   Replace the DEF Filter

   Remove the DEF pump filter housing and replace the internal DEF filter cartridge. A clogged filter is a primary cause of pressure buildup failure.

4. 4

   Service the Doser/Injector

   Inspect the DEF doser/injector at the exhaust. If it is blocked with crystallized urea, clean it with warm water or replace it.

5. 5

   Replace the DEF Pump Module

   If the lines are airtight, the filter is new, the injector is clear, and the system still fails to build pressure, the internal pump mechanism has likely failed. Replace the DEF pump/head module.

6. 6

   Clear Codes and Test

   Use a diagnostic scan tool to clear the U 520260 code. Run the engine and monitor the actual urea pressure versus the commanded pressure to verify the repair.