Case IH F-157-12 - ECU – Engine Control Unit (ECU): Fuel rail pressure sensor voltage is lower than expected

This fault code indicates that the voltage signal returning from the fuel rail pressure sensor to the control module has dropped below the normal operating range. This means the sensor is either failing internally, there is a wiring issue (such as a short to ground or an open circuit), or the actual fuel pressure in the common rail has dropped so low that the sensor's output voltage is out of bounds.

• MAGNUM AFS Connect
• Magnum (235, 250, 280, 310, 340, 380)
• Steiger / Quadtrac (470, 500, 540, 580, 600, 620)
• Puma (115 through 240)
• Optum (270, 300)
• Maxxum series
• Combine 5140
• Combine 6140
• Combine 7140
• Patriot 2240
• Patriot 3230
• Patriot 3330
• SPX3320
• 580N backhoe
• 580SN backhoe
• 590SN backhoe
• 521E through 921F wheel loaders
• 1150K crawler dozer
• 1850K crawler dozer

1. 1

   With the key ON and engine OFF, back-probe the fuel rail pressure sensor. The signal wire should typically output around 0.5 volts. If it does not, the sensor may be faulty.

2. 2

   Verify that the ECU is supplying a steady 5-volt reference to the sensor. Next, check the ground circuit; there should be less than 50 mV on the sensor ground wire.

3. 3

   Inspect the wiring harness between the sensor and the ECU for chafing, pinched wires, open circuits, or a short to ground.

4. 4

   Ensure the low voltage isn't a symptom of actual low fuel pressure. Check for restricted/plugged fuel filters, a failing high-pressure fuel pump, or a stuck-open fuel pressure relief valve.

1. 1

   Preparation

   Turn off the machine, remove the key, and disconnect the battery to prevent accidental electrical spikes.

2. 2

   Clean the Area

   Thoroughly clean the area around the fuel rail and the sensor. The high-pressure common rail system is extremely sensitive to dirt and contamination.

3. 3

   Removal

   Disconnect the 3-pin electrical connector from the sensor. Carefully unscrew the old sensor from the fuel rail.

4. 4

   Installation

   Thread the new fuel rail pressure sensor into the rail. Torque it to the manufacturer's exact specification (refer to your specific engine's service manual, as over-tightening can damage the rail and under-tightening will cause high-pressure leaks).

5. 5

   Reassembly

   Reconnect the electrical connector and reconnect the battery.

6. 6

   Testing

   Turn the key to the ON position to prime the fuel system. Start the engine, check for any fuel leaks around the sensor threads, and use a diagnostic tool to clear the F-157-12 fault code.