Case IH 12023 – INST2 (Instrumentation Controller 2) / AUX89: Communications Lost with Aux89 Controller

The system is unable to detect or communicate with the controller responsible for operating the 8th and 9th auxiliary remote hydraulic valves. In some modules, this code indicates an Invalid Source Address Controller, meaning the module is broadcasting an unrecognized or conflicting address on the network.

• STX Steiger
• TJ Series
• Steiger
• Magnum
• Puma

1. 1

   Verify Power and Ground: Check the battery voltage, fuses, and the valve supply relays powering the AUX89 controller.

2. 2

   Inspect the Wiring Harness: Trace the CAN bus wiring between the INST2 (Instrumentation) controller and the AUX89 controller. Look for chafed wires, pinch points, or rodent damage.

3. 3

   Check Connectors: Disconnect the harness at the AUX89 controller. Inspect for pushed-back pins, corrosion, moisture intrusion, or loose terminal tension.

4. 4

   Test CAN Bus Integrity: Use a multimeter to check the CAN High and CAN Low lines for proper voltage (typically around 2.5V) and verify the CAN bus terminating resistors (should read approximately 60 ohms across the network when powered down).

1. 1

   Disconnect Battery

   Always disconnect the negative battery terminal before performing electrical repairs to prevent short circuits.

2. 2

   Clean and Reseat Connections

   If corrosion or moisture is found at the AUX89 connector, clean the pins with electrical contact cleaner, apply dielectric grease, and firmly reconnect the harness.

3. 3

   Repair Wiring

   If continuity tests reveal an open or shorted CAN wire, splice and heat-shrink the damaged section of the harness according to OEM wiring repair standards.

4. 4

   Replace the Controller (If Necessary)

   If the wiring harness, power, and ground are all verified as good, the AUX89 controller itself has likely suffered an internal logic failure. Remove the mounting bolts, disconnect the hydraulic valve solenoids and main harness, and install the new controller.

5. 5

   Clear Codes and Calibrate

   Reconnect the battery. Use the Case IH Electronic Service Tool (EST) to clear the inactive 12023 fault code. If a new AUX89 controller was installed, it must be configured and calibrated to the tractor's CAN network using the EST software.