Case IH F-157-20 - ECU – Engine Control Unit (ECU): Rail pressure sensor value is above maximum offset

The raw pressure value reported by the fuel rail pressure sensor is higher than the maximum allowed tolerance threshold when the engine is just starting or immediately after stopping. This indicates that the sensor's baseline reading has drifted out of calibration or there is a wiring issue.

• MAGNUM AFS Connect
• Magnum series (e.g., 7220)
• Steiger series (e.g., 430)
• Maxxum series (110, 115, Multicontroller, CVX)
• Farmall series (75A, 90C, 95A, 100C, 105A, 110C, 110U, 115A, 120C, 120U)
• CVX models (140, 150, 160, 175, 195)
• 240 Series Axial-Flow Combines

1. 1

   Perform Key-On, Engine-Off (KOEO) Test: Connect a diagnostic scan tool and monitor live data for Fuel Rail Pressure. It should read near 0 psi/bar. An artificially high reading indicates sensor drift.

2. 2

   Inspect the 3-pin connector at the fuel rail pressure sensor for pushed-out pins, corrosion, or moisture.

3. 3

   Verify the 5V reference supply from the ECU to the sensor.

4. 4

   Verify the sensor ground circuit.

5. 5

   Check the signal wire for a short-to-voltage, which would cause an artificially high reading.

6. 6

   If the wiring, 5V reference, and ground are all within specification but the KOEO pressure reading remains high, the sensor itself is internally faulty and must be replaced.

1. 1

   Preparation

   Turn off the ignition, remove the key, and disconnect the negative battery cable. Allow the engine to cool completely.

2. 2

   Relieve Pressure

   Ensure the high-pressure fuel system has depressurized. (Wait at least 10-15 minutes after shutting off the engine before opening the fuel system).

3. 3

   Locate the Sensor

   Locate the fuel rail pressure sensor, which is threaded directly into the high-pressure common fuel rail on the engine block.

4. 4

   Clean the Area

   Thoroughly clean the area around the sensor with brake parts cleaner and compressed air. It is critical that no dirt or debris enters the open fuel rail.

5. 5

   Removal

   Disconnect the electrical harness from the sensor. Use the appropriate wrench (typically 27mm) to unthread and remove the faulty sensor from the rail.

6. 6

   Installation

   Thread the new fuel rail pressure sensor into the rail by hand to prevent cross-threading. Torque the sensor to the exact OEM specification listed in your engine's service manual (over-tightening can damage the rail; under-tightening will cause high-pressure leaks).

7. 7

   Reassembly

   Reconnect the electrical harness until it clicks securely. Reconnect the battery.

8. 8

   System Bleeding

   Turn the key to the ON position for 30 seconds without starting the engine to allow the electric lift pump to prime the system. Repeat this cycle 2-3 times to bleed air from the low-pressure side.

9. 9

   Verification

   Start the engine and check for fuel leaks around the new sensor. Use a diagnostic tool to clear the F-157-20 fault code and verify that the live rail pressure readings are now within normal parameters.