Case IH F-677-03 - ECU – Engine Control Unit (ECU): Starter relay high side driver circuit short to battery failure

The control module has detected that the voltage on the high side (power supply side) of the starter relay driver circuit is higher than expected, indicating a short circuit directly to the battery voltage. This condition prevents the ECU from properly controlling the starter relay, which can result in a no-start condition or the starter motor engaging continuously/idling.

• MAGNUM AFS Connect
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Magnum Series (Magnum 235, 260, 290, 315, 340, 380)
• Case IH 9900 Sugar Cane Harvesters

1. 1

   Disconnect the battery and visually inspect the wiring harness from the Engine ECU to the starter relay for chafing, melted insulation, or pinched wires that could cause a short to a 12V/24V battery source.

2. 2

   Remove the starter relay and test it for internal shorts or sintered (welded/stuck) contacts.

3. 3

   Test the ignition switch circuit to ensure it is not shorted, which can inadvertently send constant battery voltage to the relay driver circuit.

4. 4

   Using a multimeter, perform a harness pin-out test to check the continuity of the high-side driver wire between the ECU harness connector and the relay block. Verify there is no voltage present on this wire when the key is off or in the run position.

1. 1

   Isolate Power

   Turn off the master disconnect switch or disconnect the negative battery terminal to prevent accidental cranking or electrical arcing.

2. 2

   Access the Relay Panel

   Locate the main electrical distribution box or relay panel (location varies by model; on Magnum tractors, this is often near the cab firewall or side console).

3. 3

   Repair Wiring (If Applicable)

   If the diagnostic tests revealed a short in the wiring harness, splice and solder the damaged section of the wire, and seal it with heat-shrink tubing. Reroute the harness away from sharp metal edges or high-heat sources.

4. 4

   Replace the Starter Relay

   If the wiring is intact but the relay failed the diagnostic test (or if you are replacing it as a preventative measure due to contact sintering), pull the old relay and insert the new OEM replacement.

5. 5

   Reassemble and Clear Codes

   Reconnect the battery. Turn the ignition key to the ON position and use a diagnostic scan tool (or the machine's onboard diagnostic display) to clear the F-677-03 / 3258 fault code.

6. 6

   Test Operation

   Attempt to start the machine to verify the starter engages and disengages properly without throwing the code again.