Case IH 3987 – Engine ECU (ISM-IDI ENGINE): Fuel Solenoid Position Sensor Low Voltage

The Engine Control Unit (ECU) is receiving a voltage signal from the fuel solenoid/rack position sensor that has fallen below the minimum acceptable range. This typically points to a short to ground in the signal circuit, an open circuit, or an internal failure of the sensor itself.

• skid steer
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)
• SR175
• Steiger
• Maxxum

1. 1

   Visually inspect the wiring harness running from the fuel pump rack position sensor to the Engine ECU for chafed wires, melted insulation, or pinched areas that could cause a short to ground.

2. 2

   Disconnect the sensor harness and inspect the pins on both the sensor and the harness side for corrosion, moisture, or bent pins that could cause an open circuit or voltage drop.

3. 3

   Turn the key to the ON position (engine off) and use a multimeter to verify that the sensor is receiving the proper reference voltage (typically 5V) and has a solid ground connection from the ECU.

4. 4

   Check the continuity of the signal wire from the sensor connector back to the Engine ECU pin to ensure there is no break in the wire.

1. 1

   Power down the machine, remove the key, and disconnect the negative battery cable for safety.

2. 2

   Locate the fuel injection pump assembly on the engine block to access the Fuel Solenoid Position Sensor (Rack Position Sensor).

3. 3

   Depress the locking tab and disconnect the electrical harness from the sensor.

4. 4

   Remove the retaining bolts/screws securing the sensor to the fuel pump housing and carefully extract the old sensor.

5. 5

   Clean the mounting surface. Install the new OEM sensor and tighten the fasteners to the manufacturer's specified torque.

6. 6

   Reconnect the electrical harness, ensuring the weather-pack seal is intact and the connector clicks into place.

7. 7

   Reconnect the battery.

8. 8

   Connect the Electronic Service Tool (EST) or use the machine's enhanced keypad setup menu to clear the stored 3987 error code.

9. 9

   Start the engine and verify that the Red master warning light is extinguished and the engine fuels correctly.