Case IH 3960 – Engine ECU (ISM-DI): ISM-DI Injector 2 And/Or 3 - Shorted To Low Source

The Engine Control Unit (ECU) has detected a short circuit to ground (low source) on the electrical circuit that controls fuel injector 2 and/or 3. This prevents the ECU from properly firing the affected injectors, resulting in a misfire, rough running, or the engine shutting down to protect the fuel system.

• skid steer
• SR130
• SR160
• SR175
• SV185
• 410
• 420
• 420CT
• D33
• DX31
• DX33
• D35
• DX34
• DX35
• D45
• DX45
• DX48
• DX55
• DX60
• Farmall 31
• Farmall 35
• Farmall 45
• Farmall 45A
• Farmall 45B
• Farmall 50
• Farmall 50B
• Farmall 60

1. 1

   Visual Harness Inspection: Carefully inspect the engine wiring harness routing from the Engine ECU to injectors 2 and 3 for chafing against the engine block or rodent damage.

2. 2

   Wiring Continuity Test: Disconnect the injector harness from both the ECU and the injectors. Use a multimeter to check for continuity to ground on the power and ground pins for injectors 2 and 3. If continuity to ground is present, the harness is shorted.

3. 3

   Injector Resistance Test: Disconnect the electrical connectors at injectors 2 and 3. Measure the resistance across the injector pins, and then measure from each pin to the metal body of the injector. If there is continuity to the injector body, the injector solenoid is internally shorted and must be replaced.

4. 4

   ECU Pin Check: If the wiring and injectors test good, check the ECU pins for corrosion or damage. An internal short in the Engine ECU power stage is rare but possible.

1. 1

   Safety First

   Turn off the machine, remove the key, and disconnect the negative battery cable.

2. 2

   Access the Fuel System

   Open the engine compartment and remove any covers necessary to access the fuel rail and injectors.

3. 3

   Address Wiring (If Applicable)

   If the diagnostic checks revealed a shorted harness, repair the damaged wire sections using weather-sealed connectors, or replace the entire engine wiring harness.

4. 4

   Replace Injector (If Applicable)

   Disconnect the electrical connector from the faulty injector. Clean the area around the injector to prevent debris from falling into the cylinder. Loosen and remove the high-pressure fuel line connecting the fuel rail to the injector. Cap the rail fitting. Remove the injector hold-down clamp/bolt. Carefully pull the injector from the cylinder head. Ensure the old copper sealing washer is removed with it. Install the new injector with a new copper sealing washer and O-ring. Torque the hold-down clamp and high-pressure fuel lines to OEM specifications.

5. 5

   Reassembly

   Reconnect the injector electrical connectors and the battery.

6. 6

   Clear Codes & Test

   Use a diagnostic scan tool to clear fault code 3960. Prime the fuel system if lines were opened, start the engine, and verify that the misfire is gone and the code does not return.