Massey Ferguson U 520276 – SCR / NOx Control Unit: Power supply voltage

The system monitors the voltage supplied to the module, and this code triggers when the voltage is outside the expected parameters. Sub-codes indicate a shortcut to Battery + (voltage too high) or a shortcut to Ground (voltage too low).

• 8600 Series
• 8650
• 8660
• 8670
• 8680
• 8690

1. 1

   Inspect the tractor's battery terminals to ensure they are secure, free from dirt, and not corroded. Verify the overall battery voltage is stable.

2. 2

   Using a multimeter, check the power supply voltage at the SCR/NOx control module connector. Verify that the module is receiving the correct rated voltage (typically 12V).

3. 3

   Based on the sub-code (3 or 4), test the power supply wiring harness for a short circuit to the battery positive or a short circuit to ground.

4. 4

   Check the main power supply fuses and relays (including the battery isolator relay) that feed the emissions control modules. Look for blown fuses, corroded relay terminals, or faulty switches.

1. 1

   Power Down

   Turn off the tractor ignition and disconnect the battery to ensure safety while working on the electrical system.

2. 2

   Inspect the Harness

   Locate the wiring harness leading to the SCR/NOx control unit. Visually inspect for chafed wires, melted insulation, or water ingress at the connectors.

3. 3

   Test and Replace Relays/Fuses

   Test the power supply relays and battery isolator relays. If a relay fails to click or lacks continuity across its load terminals when energized, replace it. Replace any blown fuses.

4. 4

   Repair Wiring

   If a short to ground or short to battery positive is found during multimeter testing, repair or replace the damaged section of the wiring harness.

5. 5

   Module Replacement (if necessary)

   If the wiring, fuses, and relays are all in good working order and supplying the correct 12V power to the connector, but the code persists, the internal power supply unit (PSU) inside the SCR/NOx control module has likely failed. The module will need to be replaced.

6. 6

   Clear Codes

   Reconnect the battery, turn on the ignition, and use the instrument panel or a diagnostic tool to clear the fault codes. Run the tractor to verify the code does not return.