Case IH 3747 – Engine Control Unit (ECU) / EDC: Power stages, Injector: Diagnostic fault check to report that the positive test failed

The engine controller has detected an electrical failure on the positive side of the fuel injector circuit. It indicates that the power stage within the controller is unable to successfully send or verify the positive voltage signal to one or more fuel injectors, which is usually caused by a short circuit, an open circuit in the wiring, a failed injector solenoid, or an internal failure of the controller's power stage.

• Farmall
• skid steer
• F5C engines
• F5H engines
• Farmall 85C
• Farmall 95C
• Farmall 105C
• Farmall 115U
• SR200
• SR220
• SR250
• SV250
• SV300
• TR270
• TR320
• TV380

1. 1

   Visually inspect the wiring harness between the EDC/ECU and the fuel injectors for chafed wires, melted insulation, or pinched lines that could cause a short to ground or an open circuit.

2. 2

   Disconnect the injector connectors and the EDC connectors. Check for corrosion, bent pins, or moisture intrusion.

3. 3

   Use a multimeter to measure the resistance across the terminals of each fuel injector to ensure the internal solenoids are not shorted or open.

4. 4

   Test the positive circuit lines from the EDC harness connector to the injector connectors for continuity and verify they are not shorted to ground.

5. 5

   Verify that the EDC is receiving proper system voltage and has clean, secure ground connections, as power supply issues can trigger false power stage faults.

1. 1

   Disconnect Power

   Disconnect the negative battery cable before servicing the engine electrical system.

2. 2

   Repair Wiring

   If the diagnostic checks reveal a short or open circuit in the wiring harness, repair the damaged section of the wire or replace the injector wiring harness entirely.

3. 3

   Replace Faulty Injectors

   If an injector fails the resistance test, remove the high-pressure fuel lines and the injector hold-down clamp, then extract the faulty injector. Install the new injector with new sealing rings/washers.

4. 4

   Program Injector Codes

   If an injector is replaced, you must use a Case IH diagnostic service tool (EST) to write the new injector's IMA calibration code (usually a 9-digit code printed on the injector body) into the EDC.

5. 5

   Replace/Reprogram EDC

   If the wiring and injectors test perfectly but the 3747 code persists, the EDC's internal power stage has likely failed. The official service procedure dictates to "Reload Engine Dataset or Replace Engine Controller if fault persists." If the EDC is replaced, you must use the service tool to restore self-learning parameters and injector codes.

6. 6

   Clear Codes

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