New Holland ENG 3956 – Engine Control Unit (ECU): COM1 Output Short to Battery TWV1or3 Output Short to Battery

The Engine Control Unit has detected a short to battery voltage on the COM1 circuit, which is the common power/drive circuit for the Two-Way Valves (TWV) on the common rail fuel injectors (specifically Injectors 1 and 3). A short to battery indicates that the wiring harness or the internal injector solenoid is improperly exposed to a continuous high-voltage source, preventing the ECU from correctly pulsing the injectors and causing a misfire or engine shutdown.

• L213
• L215
• L218
• L220
• L316
• L318
• L320
• C227
• C232
• C238
• SR130
• SR160
• SR175
• SV185

1. 1

   Inspect the engine wiring harness between the Engine ECU and the fuel injectors (focusing on Injectors 1 and 3) for chafed wires, melted insulation, or areas rubbing against a power source or engine block.

2. 2

   Disconnect the electrical connectors at the affected injectors, turn the key to the ON position (engine off), and use a multimeter to measure voltage at the COM1 pins to check for improper battery voltage (12V).

3. 3

   Measure the resistance across the pins of the injector solenoids (TWV1 and TWV3) and compare the readings to a known good injector (e.g., Injector 2) to check for an internal short.

4. 4

   Disconnect the harness from the Engine ECU and check the pins for corrosion, water intrusion, or bent pins that could be bridging a power circuit to the COM1 driver.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the negative battery cable to prevent electrical damage during repair.

2. 2

   Harness Repair

   If the diagnostic checks revealed a short to battery in the wiring harness, carefully open the wire loom, locate the damaged wire for the COM1 circuit, and repair it using proper soldering and heat-shrink tubing. Re-loom and secure the harness away from heat sources and sharp edges.

3. 3

   Injector Replacement

   If an injector solenoid tested as internally shorted, remove the high-pressure fuel lines and the hold-down clamp for the affected injector. Remove the faulty injector and install a new OEM injector with new copper sealing washers and O-rings. Torque the hold-down and fuel lines to OEM specifications.

4. 4

   ECU Replacement

   If the harness and injectors test perfectly fine, the Engine ECU may have suffered an internal short on the COM1 driver circuit. Replace the ECU and flash it with the correct software dataset using the New Holland Electronic Service Tool (EST).

5. 5

   Clear Codes

   Reconnect the battery, turn the key ON, and use a diagnostic scan tool or DTC eraser to clear the ENG 3956 fault code. Start the engine and verify smooth operation without the code returning.