Case IH 3438 – Engine Control Unit (ECU A-095): Auxiliary power relay high side driver circuit short to ground failure

The Engine Control Unit (ECU) controls the voltage supplied to the auxiliary power relay (designated in wiring diagrams as the K-064 relay). The ECU actively monitors the high side of this circuit. If the ECU detects that the K-064 high side control circuit has shorted to ground, it will log this fault code.

• Steiger T4B
• Case IH Puma Series Tractors (165, 175, 180, 195, 210, 225, 240 CVX)
• Case IH 240 Series Axial-Flow Combines (7240, 8240, 9240)

1. 1

   Use the Case IH Electronic Service Tool (EST) to check if the fault is currently active or intermittent

2. 2

   Ensure no external power supplies or aftermarket accessories have been improperly spliced into the auxiliary power circuit

3. 3

   Test the K-064 auxiliary power relay coil for internal faults or a dead short

4. 4

   Inspect the K-064 high side control circuit wiring harness between the relay block and the ECU A-095 for chafing, melted insulation, or a direct short to the chassis ground

5. 5

   Verify the alternator and charging system are operating at the correct voltage, as voltage spikes can sometimes trigger driver circuit faults

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the negative battery cable to prevent electrical spikes during testing.

2. 2

   Locate the Relay

   Access the main relay/fuse box (often located behind the operator's seat or in the right-hand console, depending on the model) and locate the Auxiliary Power Relay (K-064).

3. 3

   Test/Replace the Relay

   Remove the K-064 relay. Use a multimeter to check the resistance across the relay coil pins. If the coil is shorted or out of specification, replace the relay.

4. 4

   Trace the Circuit

   If the relay is good, use a multimeter to check for continuity to ground on the high-side driver wire running from the relay socket back to the ECU A-095 harness connector.

5. 5

   Repair Wiring

   If a short to ground is found in the wire, trace the harness physically to find the pinch point or rubbed insulation. Repair the wire and re-loom the harness.

6. 6

   ECU Re-seat/Replacement

   If the relay and wiring both test perfectly fine, the fault is likely an internal short within the ECU A-095 itself. Re-seat the ECU connectors to ensure a good connection. If the code remains active, the ECU A-095 will need to be replaced and reprogrammed by a dealer.

7. 7

   Clear Codes

   Reconnect the battery, turn the key on, and use the EST to clear the fault code and verify the repair.