Case IH 90 – Armrest Controller (ARU): Differential Lock Switch is failed in the Armrest Controller.

The controller has detected an open circuit, short circuit, or implausible signal coming from the differential lock switch located on the operator's armrest console. The switch is hardwired directly to the armrest controller, and the system disables the differential lock function to prevent unintended engagement or drivetrain damage.

• Magnum
• Case IH MX Magnum Series (MX210, MX230, MX255, MX285)
• Case IH Magnum Series (Series 4) 235 through 340
• Case IH STX Steiger / Quadtrac Series (STX375, STX425, STX440, STX450, STX500)

1. 1

   Check the Armrest Controller for secondary fault codes (e.g., ARM 1069 or 6004) indicating a CAN-BUS or Rear Diff Lock Switch failure.

2. 2

   Inspect the connector ends at the switch and the armrest controller for damaged, bent, pushed-back, or dislocated pins.

3. 3

   Test the switch to verify if it has failed mechanically or electrically (e.g., stuck contacts).

4. 4

   Inspect the wiring harness inside the armrest for chafing or pinch points that could cause a short to ground or an open circuit.

5. 5

   Verify the overall function of the armrest controller to ensure it isn't a broader printed circuit board (PCB) failure.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the battery to prevent electrical shorts while working inside the armrest console.

2. 2

   Access the Armrest Console

   Remove the retaining screws securing the top cover or side panel of the right-hand armrest control console.

3. 3

   Remove the Faulty Switch

   Locate the Differential Lock Switch. Depress the retaining tabs on the sides of the switch body and push it up/out of the console bezel.

4. 4

   Disconnect the Harness

   Carefully unplug the wiring harness connector from the bottom of the switch.

5. 5

   Install the New Switch

   Plug the wiring harness into the new OEM switch, ensuring the connector clicks securely into place. Snap the new switch down into the armrest bezel.

6. 6

   Reassemble and Test

   Reinstall the armrest covers and screws. Reconnect the battery, turn the key on, and clear the stored fault codes. Test the differential lock engagement to ensure Code 90 does not return.