Massey Ferguson 157.15 – Engine ECU (EEM4): Fuel Rail Pressure Below Requested Pressure (ECU) / Rail pressure controller, Positive deviation.

The engine control module is commanding a specific fuel pressure in the common rail, but the actual pressure measured by the fuel rail pressure sensor is lower than the target. The "Positive deviation" indicates that the controller is having to positively deviate (increase its output command to the fuel pump/valves) to try and compensate for the lack of pressure.

• 4710
• 7724S
• 5712SL
• Interim Tier 4 (2012-2015)
• 7722
• 7722S
• 7615
• 5613
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 7616
• 7618
• 5608
• 4708
• 7619
• 7626
• 7726S
• 7624
• 4707
• 4709
• 5711SL
• 7614
• 7718S
• 5610
• 7620
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 5612
• 7622
• 7720
• Tier 4 (2015-2021)
• 5611
• 7715S
• 5609
• 7724
• 4700 Series
• 5600 Series
• 6600 Series
• 6612-6616
• 7600 Series
• 7615-7626
• 8600 Series
• 8650-8690
• 8700 Series
• 8727-8737

1. 1

   Low-Pressure Fuel System: Check for fuel starvation. Inspect the primary and secondary fuel filters for clogging, water contamination, or gelling. Ensure the low-pressure lift pump is supplying adequate fuel to the high-pressure pump.

2. 2

   Visual & Harness Inspection: Inspect the wiring harness and connector at the Fuel Rail Pressure Sensor for corrosion, chafing, or loose pins.

3. 3

   Leak-Off / Return Flow Test: A common cause of low rail pressure is fuel escaping back to the return system. Test the fuel injectors for excessive return flow (leak-off).

4. 4

   Pressure Relief Valve Check: Check the mechanical fuel pressure relief valve on the fuel rail. If this valve is weak or stuck open, it will bleed high-pressure fuel back into the return line, preventing the rail from reaching the requested pressure.

1. 1

   Filter Replacement

   Start by replacing the fuel filters and bleeding the low-pressure fuel system to rule out basic fuel starvation.

2. 2

   Sensor Verification

   Using a diagnostic scan tool, monitor the live fuel rail pressure data. If the sensor reading is erratic or drops out entirely, replace the Fuel Rail Pressure Sensor.

3. 3

   Address Leaks

   If the leak-off test reveals an injector with excessive return flow, replace the faulty injector and program the new injector trim codes into the EEM4 ECU.

4. 4

   Relief Valve Replacement

   If the fuel pressure relief valve is found to be leaking fuel into the return line under normal operating pressures, depressurize the fuel system and replace the relief valve. Note: Extreme cleanliness is required when opening the high-pressure fuel system; even microscopic contamination can destroy common rail components.

5. 5

   High-Pressure Pump

   If the low-pressure supply is good, the sensor is accurate, and there are no leaks in the injectors or relief valve, the high-pressure fuel pump is likely failing and must be replaced.

6. 6

   Clear and Test

   Clear the 000157.15 fault code from the EEM4 ECU using a diagnostic tool and test drive the tractor under heavy load to verify the rail pressure meets the requested target.