Case IH 3439 – Engine Control Unit (ECU) A-095: Auxiliary power relay low side driver circuit open failure

The Engine Control Unit (ECU) controls the voltage to the auxiliary power relay (designated as K-064). The ECU continuously monitors the K-064 low side circuit for an open circuit condition. If the ECU detects an open circuit on this low side control circuit, it triggers this fault.

• Steiger T4B
• Case IH Puma Series Tractors
• Case IH 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Case IH A8000 / A8800 Series Sugar Cane Harvesters

1. 1

   Connect the Case IH Electronic Service Tool (EST) to verify if the fault code is currently active (inactive faults may indicate intermittent wiring issues)

2. 2

   Remove the K-064 Auxiliary Power Relay and test the resistance across the relay coil pins to ensure it is not internally open

3. 3

   Inspect the wiring harness between the K-064 relay socket (low side circuit) and the ECU A-095 for broken wires, rubbed-through insulation, or pushed-out pins

4. 4

   Verify if the ECU A-095 has the latest software calibration, as software errors can falsely flag circuit faults

1. 1

   Power Down

   Turn off the machine and disconnect the battery ground to ensure safety while testing electrical circuits.

2. 2

   Test/Replace the Relay

   Access the main fuse and relay panel. Locate relay K-064. Swap it with a known good relay of the same type (or test its coil resistance). If the fault clears or the coil tests open, replace the K-064 relay.

3. 3

   Repair the Wiring Harness

   If the relay is functional, use a multimeter to perform a continuity test on the low side driver wire from the relay block to the ECU A-095 connector. Repair any breaks, clean corroded grounds, and ensure the terminal pins are seated tightly in their connectors.

4. 4

   Address the ECU

   If the relay and wiring harness both test perfectly, the fault lies within the Engine Control Unit (A-095). Reconnect the battery, connect the EST, and attempt to reflash/update the ECU software. If the hardware driver inside the ECU is burnt out and cannot be recovered, the ECU A-095 must be replaced.