Case IH 3961 – ENGINE ECU: Injector 2 And 3 - Open Circuit

The engine control system has detected an open circuit (a broken electrical connection or infinite resistance) on the COM2 output circuit, which provides power/ground signals to the fuel injectors for cylinders 2 and 3. This prevents the injectors from firing, leading to engine misfires, rough running, or a severe loss of power and throttle response.

• skid steer
• SR130
• SR160
• SR175
• SV185
• 410
• 420
• D33
• DX31
• D45
• DX48
• Farmall 31
• Farmall 60
• Magnum 250
• Steiger

1. 1

   Visually inspect the wiring harness between the Engine ECU and fuel injectors 2 and 3 for chafing, breaks, or melted insulation.

2. 2

   Disconnect the electrical plugs at Injectors 2 and 3. Check for loose, backed-out, or heavily corroded pins.

3. 3

   Using a multimeter, measure the resistance across the two terminals on Injector 2 and Injector 3. If the reading shows infinite resistance (OL), the injector solenoid is internally open.

4. 4

   Check the continuity of the COM2 circuit (TWV2 and TWV4 pins) from the injector connectors back to the Engine ECU harness plug.

1. 1

   Turn off the machine, remove the key, and disconnect the negative battery cable to prevent electrical shorts.

   Turn off the machine, remove the key, and disconnect the negative battery cable to prevent electrical shorts.

2. 2

   Locate the Engine ECU and trace the wiring harness to the fuel rail and injectors on the engine block.

   Locate the Engine ECU and trace the wiring harness to the fuel rail and injectors on the engine block.

3. 3

   Disconnect the electrical connectors at cylinder 2 and cylinder 3 injectors.

   Disconnect the electrical connectors at cylinder 2 and cylinder 3 injectors.

4. 4

   If the diagnostic tests revealed a broken wire in the harness, repair the wire using OEM-approved splicing techniques or replace the engine wiring harness section.

   If the diagnostic tests revealed a broken wire in the harness, repair the wire using OEM-approved splicing techniques or replace the engine wiring harness section.

5. 5

   If the diagnostic tests revealed an internally open injector, relieve the fuel system pressure.

   If the diagnostic tests revealed an internally open injector, relieve the fuel system pressure.

6. 6

   Remove the high-pressure injection pipe connecting the fuel rail to the faulty injector(s).

   Remove the high-pressure injection pipe connecting the fuel rail to the faulty injector(s).

7. 7

   Remove the injector hold-down clamp and extract the faulty injector.

   Remove the injector hold-down clamp and extract the faulty injector.

8. 8

   Install the new injector with a new copper sealing washer and O-rings. Torque the hold-down clamp and high-pressure fuel lines to OEM specifications.

   Install the new injector with a new copper sealing washer and O-rings. Torque the hold-down clamp and high-pressure fuel lines to OEM specifications.

9. 9

   Reconnect the electrical connectors and the battery.

   Reconnect the electrical connectors and the battery.

10. 10

    Connect an Electronic Service Tool (EST) to clear the 3961 fault code, prime the fuel system, and run the engine to verify the repair.

    Connect an Electronic Service Tool (EST) to clear the 3961 fault code, prime the fuel system, and run the engine to verify the repair. (Note: Depending on the exact engine, you may need to write the new injector's QR calibration code to the ECU to prevent subsequent codes like 3967 or 3968).