Case IH 3113 – Engine Control Module (ECM / EDC): Main Relay 1 (High Pressure Pump - power supply to the fuel metering unit) - Short to Battery

The Engine Control Module (ECM) has detected a 'short to battery' (unintended constant 12V power) on the circuit that supplies power to the fuel metering unit via Main Relay 1. This prevents the ECM from properly pulse-width modulating the valve, leading to fuel pressure deviations, engine stalling, or a no-start condition.

• Magnum series (235–340 Series 4)
• Puma series
• Steiger series
• Maxxum models
• 580 Super N
• 621C
• 721
• 821

1. 1

   Relay Inspection: Locate Main Relay 1 in the machine's power distribution/fuse box. Check if the relay contacts have fused closed, which would send constant battery voltage to the metering unit.

2. 2

   Wiring Harness Test: Disconnect the harness at the fuel metering unit and at the ECM. Use a digital multimeter to test the power supply wire for continuity to a 12V power source (Short to Battery). Inspect the wiring loom for melted insulation or chafing against the engine block or other live wires.

3. 3

   Connector Inspection: Check the electrical connector at the fuel metering unit on the high-pressure pump for oil/diesel contamination, water ingress, or damaged pins that could bridge the power circuit.

4. 4

   Component Resistance Test: Test the internal resistance of the fuel metering unit solenoid. An internal short inside the solenoid coil can sometimes trigger this circuit fault.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the negative battery cable to prevent further electrical damage during testing.

2. 2

   Swap the Relay

   Swap Main Relay 1 with a known-good relay of the exact same type (e.g., the horn or work light relay). Reconnect the battery, clear the codes, and cycle the key. If the code changes to a different state or clears, replace the faulty relay.

3. 3

   Repair the Harness

   If the relay is good but the multimeter shows voltage on the signal wire when it should be dead, trace the wiring harness back to the ECM. Locate the shorted section of the wire and splice in a repair, or replace the affected engine harness section.

4. 4

   Replace the Fuel Metering Unit

   If the wiring and relay are completely intact and the short is isolated to the actuator itself, the fuel metering unit must be replaced. Clean the area around the high-pressure fuel pump thoroughly to prevent dirt from entering the fuel system. Remove the mounting screws holding the metering unit to the CP3 pump. Lubricate the O-rings on the new metering unit with clean diesel fuel and carefully seat it into the pump. Torque the fasteners to OEM specifications and reconnect the electrical harness.

5. 5

   Clear and Verify

   Use a diagnostic scan tool (like the CNH EST) to clear the 3113 fault code. Start the engine and monitor the desired vs. actual fuel rail pressure to ensure the new metering unit is responding correctly.