Massey Ferguson 157.21 – Engine ECU (EEM4): Fuel Rail Pressure Is Not As Expected During Startup Or Shutdown

Rail pressure raw value is below minimum offset, meaning the engine control system is detecting that the fuel pressure in the common rail is dropping below the minimum acceptable threshold when the engine is either trying to start or shutting down.

• 7724S
• 5712SL
• Interim Tier 4 (2012-2015)
• 7722S
• 7722
• 7615
• 5613
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 7616
• 7618
• 5608
• 7619
• 7626
• 7726S
• 7624
• 5711SL
• 7614
• 7718S
• 5610
• 7620
• 7719
• 7714
• 7716S
• 5612
• 7622
• 7720
• Tier 4 (2015-2021)
• 5611
• 7715S
• 5609
• 7724
• 7600 Series
• 5600 Series
• 6600 Series
• 8600 Series

1. 1

   Check the entire high-pressure fuel system (fuel rail, injector lines, and high-pressure pump) for any visible diesel leaks that would cause a pressure drop.

2. 2

   Inspect the wiring harness and the 3-pin connector going to the fuel rail pressure sensor for chafed wires, corrosion, or loose pins that could cause an intermittent or low voltage signal.

3. 3

   Ensure the low-pressure lift pump is supplying adequate fuel to the high-pressure pump and that fuel filters are not restricted.

4. 4

   Check if the fuel pressure relief valve (PRV) on the rail is prematurely opening or leaking fuel back to the return line.

1. 1

   Safety First

   Turn off the tractor, remove the key, and allow the engine to cool. Crucial: Wait for the high-pressure fuel system to depressurize completely before opening any lines to avoid severe injury from high-pressure fuel spray.

2. 2

   Locate the Sensor

   Locate the fuel rail pressure sensor, which is threaded directly into the high-pressure fuel rail.

3. 3

   Disconnect Wiring

   Carefully unplug the 3-pin electrical connector from the sensor.

4. 4

   Remove the Sensor

   Using the appropriate wrench, unscrew the faulty sensor from the fuel rail. Have a rag ready to catch any residual fuel.

5. 5

   Install the New Sensor

   Thread the new sensor (e.g., M14 x 1.5 or M18 x 1.5 thread depending on exact rail spec) into the fuel rail and torque it to the manufacturer's exact specification.

6. 6

   Reconnect

   Plug the 3-pin electrical connector back into the new sensor.

7. 7

   Prime and Test

   Turn the key to the ON position to allow the lift pump to prime the system. Check for leaks around the new sensor. Start the engine, clear the active 000157.21 / SPN 157 FMI 21 fault code using a diagnostic service tool, and verify that the code does not return during startup or shutdown.