Case IH 3114 – Engine Control Module (ECM / EDC): Main Relay 1 (High Pressure Pump - power supply to the fuel metering unit) Short to Ground

The Engine Control Module (ECM) has detected that the electrical circuit supplying power (via Main Relay 1) to the fuel metering unit is shorted to ground. This prevents the metering unit from properly regulating fuel pressure, which can lead to engine derate, failure to start, or stalling.

• Magnum 235 - 340 (Series 4)
• Steiger series
• Puma series (e.g., 210)
• MX/TG series
• Axial-Flow Combines (e.g., 240 series)
• T8.xxx Series
• T7 Series

1. 1

   Visually inspect the wiring harness running between the Engine ECM, Main Relay 1, and the fuel metering unit on the high-pressure fuel pump. Look for chafed insulation, pinched wires, or areas where the harness rubs against the engine block or chassis.

2. 2

   Remove Main Relay 1 and test it with a multimeter. Check for an internal short circuit across the load terminals or the coil.

3. 3

   Disconnect the electrical connector at the fuel metering unit on the CP3 pump. Use a multimeter to check the power supply wire for continuity to ground.

4. 4

   Test the pins on the fuel metering unit itself to ensure the internal solenoid has not shorted to its own housing.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Isolate the Short

   Based on the diagnostic checks, determine if the short is in the wiring harness, the relay, or the metering unit.

3. 3

   Repair the Harness

   If a wire is chafed and grounding out, splice in a new section of wire using weather-sealed heat shrink connectors, or replace the damaged harness section. Reroute the harness away from sharp edges or high-heat areas.

4. 4

   Replace the Relay

   If Main Relay 1 is internally shorted, plug a new OEM relay into the power distribution block.

5. 5

   Replace the Fuel Metering Unit

   If the actuator on the CP3 pump is shorted, clean the area around the high-pressure pump to prevent contamination. Remove the mounting screws holding the metering unit to the pump, remove the old unit, lubricate the O-rings on the new unit with clean diesel fuel, and install it. Torque the fasteners to OEM specifications.

6. 6

   Clear Codes

   Reconnect the battery, turn the key to the ON position, and use a diagnostic service tool (like the CNH Electronic Service Tool) to clear the inactive 3114 fault code.

7. 7

   Test Run

   Start the engine and verify that fuel rail pressure is stable and the code does not return.