Massey Ferguson U 520310 – Engine ECU / SCR Dosing Control Module: Urea box temperature - physical error: Urea Temperature too high or too low.

This code indicates that the temperature sensor inside the Diesel Exhaust Fluid (DEF) / Urea tank is reporting a value that is physically impossible or out of the expected operating range. This usually points to a failed temperature sensor, a wiring issue, or a problem with the DEF tank heating system.

• 8600 Series
• 8650
• 8660
• 8670
• 8680
• 8690
• 5600 Series
• 6600 Series
• 7600 Series
• 8700 Series

1. 1

   Inspect the DEF/Urea tank sensor harness and connector. Look for corrosion, moisture, or pushed-out pins, which are common in harsh agricultural environments.

2. 2

   Check the wiring harness between the DEF tank sender unit and the Engine ECU for open wires or short circuits to ground/battery.

3. 3

   Connect a diagnostic scan tool (like the AGCO EDT) and observe the live data for the DEF tank temperature. If the reading is pegged at an extreme value (e.g., -40°C or +150°C), the sensor itself has likely failed.

4. 4

   Verify that the engine coolant valve that supplies heat to the DEF tank isn't stuck open, which could genuinely cause the urea to overheat.

1. 1

   Preparation

   Turn off the tractor, disconnect the battery, and thoroughly clean the top of the DEF tank around the sender unit. DEF systems are highly sensitive to contamination; dirt entering the tank can destroy the SCR injector.

2. 2

   Disconnect Lines

   Carefully unplug the electrical harness connector from the DEF sender unit. Disconnect the DEF supply and return lines (have a clean rag ready to catch any spilled urea fluid).

3. 3

   Remove the Sender Unit

   Unscrew the mounting bolts or the locking ring securing the sender unit to the top of the DEF tank.

4. 4

   Extraction

   Carefully pull the sender unit assembly straight up and out of the tank.

5. 5

   Installation

   Insert the new DEF sender unit/temperature sensor assembly into the tank, ensuring the new O-ring or gasket is properly seated to prevent water/dust ingress.

6. 6

   Reassembly

   Secure the locking ring or bolts. Reconnect the DEF fluid lines and the electrical harness.

7. 7

   Verification

   Reconnect the battery. Use a diagnostic tool to clear the U 520310 fault code. Turn the key on and verify that the live DEF temperature reading is now accurate. Run the engine to ensure the system primes and no derate conditions return.