Case IH F-677-04 - ECU – Engine ECU: Starter relay high side driver circuit short to ground failure

The control unit has detected that the voltage on the high side of the starter relay circuit is below the normal operating threshold, indicating a direct short circuit to ground (earth) somewhere in the relay driver circuit.

• MAGNUM AFS Connect
• 240 Series Axial-Flow Combines (7230, 8230, 9230)
• 88 Series Combines (5088, 6088, 7088)
• 130 Series Combines (5130, 6130, 7130)
• CX Series Tractors (CX50 to CX100)
• JX Series Tractors (JX70U to JX1090U)
• MX Series Tractors (MX100 to MX135)
• Magnum Tractors
• Steiger Tractors
• Farmall Tractors
• Case N-Series Loader Backhoes
• Cotton Express 420
• Cotton Express 620

1. 1

   Visually inspect the contacts on the 'START' connector of the starter relay and the 'MOTOR' connector of the ECU for oxidation, corrosion, or looseness.

2. 2

   Perform a harness short-to-ground test: With the ignition key OFF, disconnect the ECU and the starter relay. Use a multimeter to check for continuity to ground on the high-side driver wire between the ECU and the relay.

3. 3

   Perform a relay resistance test: Remove the starter relay and measure the resistance across the relay coil pins to check for an internal short or out-of-spec resistance.

4. 4

   Verify that the main relay voltage is supplying adequate power (typically >= 10V) to the circuit when commanded.

1. 1

   Disconnect Power

   Disconnect the negative battery cable to prevent accidental cranking or further electrical damage.

2. 2

   Locate the Starter Relay

   Access the main fuse/relay panel or the auxiliary relay bracket (location varies by model, often near the firewall, steering column, or directly on the engine harness).

3. 3

   Repair Wiring

   If the diagnostic tests revealed a short to ground in the harness, trace the specific wire from the ECU to the relay. Repair the chafed insulation or splice in a new section of wire using weather-sealed heat shrink connectors.

4. 4

   Replace the Relay

   If the wiring is intact but the relay failed the resistance test, pull the old relay from the socket. Apply a small amount of dielectric grease to the terminals of the new relay and seat it firmly into the socket.

5. 5

   Reassemble and Clear Codes

   Reconnect the battery. Turn the key to the ON position and use a diagnostic scan tool to clear the F-677-04 / SPN 677 FMI 4 fault code from the Engine ECU.

6. 6

   Test Operation

   Crank the engine to verify the starter engages properly and ensure the fault code does not return.