Case IH F-2634-04 - ECU – Engine Control Unit (ECU): Auxiliary power relay low side driver circuit short to ground failure.

The control module monitors the voltage to the auxiliary power relay. FMI 04 indicates a "Voltage Below Normal, or Shorted to Low Source" condition. This means the control unit has detected that the low side driver circuit for this relay is shorting directly to the chassis ground, which can blow fuses, cause a loss of auxiliary power, or prevent the engine from starting/running properly.

• MAGNUM AFS Connect
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Magnum series (Magnum 275)
• Maxxum series (100-140)
• Puma series
• Steiger/Quadtrac models

1. 1

   Check Fuses: Locate the Main Distribution Panel (MDP) or power center and check for blown main fuses (such as MFP 2) that supply the auxiliary power relay.

2. 2

   Locate the Relay: Identify the Auxiliary Power Relay (often designated as Relay #12 in the MDP, or K-064 depending on the specific model's schematic).

3. 3

   Test for Short to Ground: Disconnect the battery, remove the auxiliary power relay and the corresponding fuse. Use a multimeter to check for continuity to ground on the non-powered side of the fuse/relay receptacle. If continuity to ground is present, there is a short in the cab main harness or engine harness between the ECU and the relay.

4. 4

   Inspect the Harness: Visually inspect the wiring harness running from the ECU to the power distribution panel. Look for chafed insulation, pinched wires, or areas where the harness rubs against the metal chassis.

1. 1

   Safety First

   Lower all hydraulic equipment to the ground, turn off the ignition, and disconnect the battery (negative terminal first) to prevent electrical spikes or fires.

2. 2

   Isolate the Fault

   Based on your multimeter continuity test, trace the specific wire (e.g., the low side driver wire from the ECU pin to the relay socket).

3. 3

   Repair the Wiring

   If a chafed or exposed wire is found shorting against the frame, repair the wire using OEM-approved heat-shrink butt connectors and re-loom the harness. Secure it away from sharp edges.

4. 4

   Replace the Relay

   If the wiring harness tests perfectly fine, the internal coil of the auxiliary power relay itself may have shorted out. Replace the relay with a new OEM unit.

5. 5

   Replace Fuses

   Replace any blown fuses in the MDP with the exact same amperage rating (do not up-size the fuse).

6. 6

   Reassemble and Clear Codes

   Reconnect the battery (positive first, then negative). Turn the ignition on, use the machine's diagnostic screen or a connected scan tool to clear the F-2634-04 fault code, and start the engine to verify the repair.