Massey Ferguson 520207.31 – Engine ECU: Rail Pressure control: Pressure BELOW normal in limp home mode

The engine's control system has detected that the actual fuel rail pressure has dropped below the minimum requested operating range while the tractor is already operating in an active derate or 'limp home' state.

• 4710
• 7724S
• 5712SL
• 7722S
• 7722
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 4708
• 7726S
• 4707
• 4709
• 5711SL
• 7718S
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 7720
• Tier 4 (2015-2021)
• 7715S
• 7724
• MF 8700 series

1. 1

   Verify adequate fuel supply by checking for clogged primary or secondary fuel filters that can starve the high-pressure pump.

2. 2

   Inspect the wiring harness for the fuel rail pressure sensor and pressure control valve for a short circuit to ground or battery voltage.

3. 3

   Check the rail pressure sensor voltage to ensure it is not reading above normal, below normal, or open circuit.

4. 4

   Test the mechanical fuel rail pressure relief valve (PRV) to see if it is stuck open or popping off prematurely.

1. 1

   Resolve Fuel Restrictions

   Replace the fuel filters and bleed the low-pressure fuel system to rule out a simple fuel starvation issue.

2. 2

   Repair Wiring

   If the diagnostic multimeter tests reveal a short to ground or a short to battery voltage in the pressure control valve circuit, repair the damaged section of the wiring harness.

3. 3

   Replace the Pressure Sensor

   If the wiring is intact but the sensor voltage is erratic or out of the measurable range, relieve the fuel system pressure and replace the Fuel Rail Pressure Sensor.

4. 4

   Replace the Pressure Relief Valve

   If the sensor is reading accurately but the rail cannot maintain pressure (and no external leaks or injector leak-offs are found), replace the Fuel Rail Pressure Relief Valve (PRV).

5. 5

   Clear Codes

   Use a specialized diagnostic tool (such as the AGCO Electronic Diagnostic Tool) to clear the DTCs from the Engine ECU and take the tractor out of limp mode. Test drive the machine under load to ensure rail pressure remains stable.