Case IH F-2634-05 - ECU – Engine Control Unit (ECU): Auxiliary power relay low side driver circuit open failure

The control module has detected an open circuit (current below normal or disconnected line) on the low side (ground-switching side) of the driver circuit that commands the auxiliary power relay. The controller is trying to energize the relay by providing a ground path, but no current flow is detected, indicating a broken wire, a disconnected plug, or a failed relay coil.

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1. 1

   Locate the Auxiliary Power Relay in the Main Distribution Panel inside the cab (often Relay #12) or the main engine fuse box

2. 2

   Visually inspect the relay terminals and ECU connectors for corrosion, pushed-out pins, or oxidation, and ensure connectors are firmly secured

3. 3

   Remove the relay and test the internal coil resistance with a multimeter (an open coil will cause this code)

4. 4

   With the relay removed and the machine powered off, check for continuity on the low-side driver wire running from the relay receptacle back to the Engine ECU harness to rule out a broken wire

5. 5

   Verify that the high side of the relay coil is receiving proper battery voltage when the key is in the ON position

1. 1

   Safety First

   Turn off the ignition. Disconnect the battery terminals (negative terminal first, then positive) to prevent accidental shorts while working on the electrical system.

2. 2

   Access the Distribution Panel

   Open the Main Distribution Panel or engine fuse box and extract the auxiliary power relay.

3. 3

   Test/Replace the Relay

   If the diagnostic checks revealed an open coil inside the relay, replace the relay with a new OEM equivalent.

4. 4

   Repair the Wiring Harness

   If the relay is functional but the circuit is open, trace the low-side driver wire from the relay block to the ECU. Locate the break or chafed wire (commonly found near harness bends or connector entries) and splice/repair the wire using weather-sealed connectors.

5. 5

   Clean Contacts

   Spray the relay socket and ECU connector pins with electrical contact cleaner to remove any light oxidation.

6. 6

   Reassembly

   Plug the relay back into the panel. Reconnect the battery terminals (positive first, then negative).

7. 7

   Clear and Verify

   Turn the ignition on, clear the inactive fault codes via the diagnostic display, and start the engine. Verify that the F-2634-05 code does not return.