Case IH 3267 – Engine ECU: Engine ECU Fuel Pump Output / Main Relay 3 - Shorted To High Source

Fault code 3267 indicates a "Short to High Source" (short circuit to battery voltage) on the output circuit controlled by Main Relay 3. Depending on the specific engine tier and configuration (such as ISM-DI or F5C engines), this circuit provides the high-side supply to either the electric fuel pump, the fuel filter heater, or the A/C compressor. The Engine Control Unit (ECU) monitors this circuit and triggers the code when it detects voltage levels above the normal operating range, indicating a short to battery power.

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1. 1

   Locate Main Relay 3 in the fuse/relay box. Inspect the relay and its socket for signs of melting, corrosion, or heat damage.

2. 2

   Use a multimeter to test the wiring harness between the Engine ECU, Main Relay 3, and the fuel pump / fuel filter heater. Check for continuity to battery positive (B+) when the circuit should be unpowered.

3. 3

   Disconnect the fuel pump and/or fuel filter heater. Check if the short to high source disappears. If it does, the component itself may be internally shorted.

4. 4

   Inspect the Engine ECU connector pins (specifically the pins for the Main Relay 3 low/high side drivers) for bent pins, moisture, or corrosion.

1. 1

   Disconnect Power

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

2. 2

   Replace Faulty Relay

   If Main Relay 3 failed testing or shows physical damage, replace it with a new OEM relay.

3. 3

   Repair Wiring

   If a short to battery voltage was found in the harness, trace the wire from the relay to the fuel pump/heater and the ECU. Repair or splice any chafed wires that are rubbing against a power source. Secure the harness with zip ties to prevent future chafing.

4. 4

   Replace Shorted Components

   If the fuel pump or fuel filter heater was found to be internally shorted, replace the faulty component.

5. 5

   Reassemble and Clear Codes

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

6. 6

   Test Operation

   Start the engine and verify that the fuel pump/heater operates correctly and that fault code 3267 does not return.