Case IH 18026 – Armrest Controller (ACM - Armrest Control Module): Rear hitch slip control potentiometer - voltage too high

The control module is receiving a signal voltage from the rear hitch slip control potentiometer that exceeds the normal operating range (above 4.8 V). This condition is typically caused by a short to power (5V or 12V) on the signal wire, an open ground circuit to the sensor, or an internal failure of the potentiometer itself.

• Magnum
• Steiger T4B
• Case IH Magnum Series: 235, 260, 290, 315, 340 (Series 4)
• Case IH Steiger / STX Series: 350, 380, 430, 450, 500, 600
• Case IH Puma Series: 165, 180, 195, 210, 225, and CVX models
• Case IH Maxxum / Farmall Series

1. 1

   Inspect the wiring harness and connectors between the rear hitch slip control potentiometer and the Armrest Controller for pinched wires, chafing, or loose/corroded pins.

2. 2

   Disconnect the potentiometer and verify the connector is receiving a steady 5V reference signal and has a solid ground connection (an open ground defaults the signal high).

3. 3

   Test the signal wire for continuity to power to ensure it is not shorted to a 12V or 5V source.

4. 4

   Measure the resistance sweep of the potentiometer while turning the dial to check for an open circuit or erratic spikes indicating internal failure.

1. 1

   Disconnect Power

   Turn the ignition OFF and disconnect the tractor's battery to prevent electrical damage while working on the CAN bus/armrest modules.

2. 2

   Access the Armrest Internals

   Carefully remove the cover panels on the right-hand operator armrest console to expose the hitch control dials and levers.

3. 3

   Remove the Faulty Sensor

   Locate the rear hitch slip control potentiometer. Disconnect its electrical harness connector.

4. 4

   Dismount the Potentiometer

   Remove the retaining nut or mounting screws securing the potentiometer to the slip control dial assembly. Pull the old sensor out.

5. 5

   Install the New Part

   Seat the new potentiometer into the dial assembly, ensuring the physical alignment tab matches the dial's position. Secure it with the mounting hardware.

6. 6

   Reassembly

   Reconnect the electrical harness and reinstall the armrest console covers.

7. 7

   Reconnect Power

   Reconnect the battery.

8. 8

   Calibration

   Turn the key ON. Use the tractor's Integrated Control Panel (ICP) or a dealer diagnostic service tool to clear the inactive 18026 fault code. You must perform a hitch/potentiometer calibration routine so the Armrest Controller can learn the new sensor's minimum and maximum voltage limits.