Case IH 3956 – Engine Control Unit (ECU): COM1 Output Short to Battery TWV1or3 Output Short to Battery / Injector 1 And/Or 4 Shorted To High Source

The engine control module has detected a short circuit to a high voltage source on the fuel injector wiring.

• ISM-DI engines
• F5C engines
• F5H engines
• Skid Steer Loaders
• SR175
• L220
• Compact Track Loaders
• tractors

1. 1

   Use a diagnostic service tool to confirm exactly which fault the ECU is reporting, as there is a discrepancy between code 3956 and the intake throttle valve description.

2. 2

   If diagnosing Code 3956 (Injector Short): Check the engine wiring harness for a short to the battery on the COM1 output (specifically Injectors 1 and 4).

3. 3

   If diagnosing Code 3956 (Injector Short): Test the injector circuits for high voltage sources.

4. 4

   If diagnosing the Intake Throttle Valve Actuator: Check the actuator relay for short circuits to ground or battery.

5. 5

   If diagnosing the Intake Throttle Valve Actuator: Verify CAN bus communication to the TVA (Throttle Valve Actuator).

6. 6

   If diagnosing the Intake Throttle Valve Actuator: Inspect the connector and wiring whip for damage, loose connections, or excessive temperature.

1. 1

   Identify the True Fault

   Connect a diagnostic service tool to the machine to verify if the active code is 3956 (Injector short) or an Intake Throttle Valve error (e.g., E82A4, 3507).

2. 2

   Inspect Wiring

   Inspect the wiring harness and connectors between the Engine ECU and the affected component (either Injectors 1/4 or the Intake Throttle Valve). Look for shorts, open loads, or whip failures.

3. 3

   Repair Harness

   Repair or replace the damaged wiring harness if a short to battery or ground is found.

4. 4

   Replace Component

   If the wiring is intact and tests fine, replace the faulty component (either the internally shorted Fuel Injector or the failed Intake Throttle Valve Actuator).

5. 5

   Clear and Test

   Once the cause of the fault code has been corrected, clear the fault code from the ECU memory and test the machine to ensure the system operates normally.