Case IH 3958 – ISM-DI: Injector 1 And 4 - Open Circuit

The engine control module has detected a break in the electrical circuit (an open load or infinite resistance) on the common output circuit (COM1) that controls the firing of fuel injectors 1 and 4.

• skid steer
• SR130
• SR160
• SR175
• SR270
• SV185
• SV300
• SV340
• TR340
• L213
• L220
• L221
• L228

1. 1

   Check for other active diagnostic trouble codes and troubleshoot those first

2. 2

   Visually inspect the engine wiring harness connecting the ISM-DI ECU to Injectors 1 and 4 for chafed wires, melted insulation, or disconnected plugs

3. 3

   Check for loose contacts or corrosion at the ECU pins (specifically the COM1 output pins) and at the injector harness connectors

4. 4

   Measure the resistance across the terminals of Injector 1 and Injector 4 to determine if the internal solenoid of either injector has failed open

1. 1

   Power Down

   Turn off the machine and disconnect the battery to prevent electrical shorts while testing the ECU and injector circuits.

2. 2

   Isolate the Open Circuit

   Using a digital multimeter, test the continuity of the wiring harness from the ISM-DI ECU connector to the plugs for Injectors 1 and 4.

3. 3

   Repair Harness

   If a break in the wire is found, repair the wiring harness or replace the injector pigtail connector.

4. 4

   Replace Injectors

   If the wiring tests good but Injector 1 or 4 shows an open internal circuit (infinite resistance), the injector must be replaced. Note: OEM guidelines highly recommend replacing fuel injectors as a complete set to prevent uneven fuel atomization.

5. 5

   Replace Engine Controller

   If both the wiring harness and the injectors test perfectly fine, the fault lies within the ISM-DI Engine Controller itself (internal failure of the COM1 output driver). The ECU will need to be replaced and reprogrammed.

6. 6

   Clear Codes

   Reconnect the battery, clear the fault codes using the diagnostic tool, and run the engine to verify the repair.