Case IH 3402 – Engine Control Unit (ECU): Rail pressure sensor: maximum rail pressure exceeded

The Engine Control Unit has detected that the fuel pressure within the common rail has spiked above the maximum allowable safety limit, or the sensor itself has failed and is falsely reporting an overpressure condition.

• Steiger
• Magnum
• Maxxum
• Farmall
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)
• Axial-Flow combines

1. 1

   Verify actual vs. commanded fuel rail pressure using an Electronic Service Tool (EST) while cranking or running to determine if the sensor is reading erratically or if the pump is over-pressurizing.

2. 2

   Inspect the wiring harness and connectors leading to the fuel rail pressure sensor and the fuel metering unit (M-PROP) for shorts to power, shorts to ground, or open circuits.

3. 3

   Check the Pressure Relief Valve (PRV) return line for excessive fuel leakage, which indicates the mechanical valve popped open due to an actual overpressure event.

4. 4

   Test sensor resistance and voltage to verify it is receiving the correct 5V reference voltage from the ECU and that the signal wire is not shorted.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the battery or remove electrical power from the ECM before servicing the fuel system.

2. 2

   Clean the Area

   Thoroughly clean the area around the fuel rail, pressure sensor, and high-pressure lines to prevent dirt from entering the sensitive common rail system.

3. 3

   Relieve Fuel Pressure

   Ensure the engine has been off long enough for the high-pressure fuel system to depressurize.

4. 4

   Replace the Sensor (If Faulty)

   If diagnostics point to a failed sensor, unscrew the old fuel rail pressure sensor from the rail and install the new one. Torque to the manufacturer's exact specifications.

5. 5

   Address the PRV (If Triggered)

   If the system genuinely over-pressurized, the mechanical pressure relief valve (PRV) on the rail was likely forced open. Once a PRV pops, it is often weakened and must be replaced to prevent low rail pressure issues later.

6. 6

   Address the Fuel Metering Unit (If Sticking)

   If the sensor is accurate and the system is actually over-pressurizing, the fuel metering unit on the high-pressure injection pump is likely stuck open. Replace the metering unit or the high-pressure pump assembly.

7. 7

   Reassemble and Clear Codes

   Reconnect all electrical connectors. Bleed the low-pressure fuel system if required. Use a diagnostic tool to clear fault code 3402 from the Engine ECU, then start the engine and verify that rail pressure remains within normal parameters.