Case IH 18270 (51875.03, 518753.04) - ACML – Armrest Control Module (ACML): Rear Hitch Height Limit Potentiometer

The "Rear Hitch Height Limit Potentiometer" monitors the operator's set limit for how high the rear 3-point hitch can be raised. When this component enters an error state, it is logged under two primary conditions: Voltage Too Low (Code 18018) or Voltage Too High (Code 18019).

• MAXXUM T4E
• VESTRUM CVX
• Case IH Magnum Series (e.g., 235 – 340 Series 4)
• Case IH Puma Series (e.g., 165, 180, 195, 210, 225 CVX)
• Case IH Steiger Series

1. 1

   Verify the Code: Check the instrument cluster or AFS Pro display to confirm if the ACML is reporting a Voltage Too Low (18018) or Voltage Too High (18019) state.

2. 2

   Inspect the Armrest Controls: Check the physical movement of the rear hitch height limit dial/slider on the armrest. Ensure it is not physically jammed or damaged.

3. 3

   Wiring and Connector Check: Inspect the wiring harness connecting the armrest potentiometers to the ACML. Look for chafed wires (which could cause a short to ground/power) or loose connector pins.

4. 4

   EHR Control Unit Check: Verify communication with the Electro-Hydraulic Remote (EHR) control unit, as related armrest dispenser control issues can sometimes trigger cascading potentiometer faults.

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the battery to prevent electrical spikes while working on the armrest console.

2. 2

   Access the ACML

   Carefully disassemble the armrest console casing to access the internal circuit boards and potentiometers.

3. 3

   Test the Potentiometer

   Use a multimeter to test the resistance sweep of the Rear Hitch Height Limit Potentiometer. If the resistance is infinite (open) or does not change smoothly as the dial is turned, the potentiometer is defective.

4. 4

   Replace the Component

   If the potentiometer is integrated into a larger valve control or armrest dispenser module, replace the faulty control assembly. If it is a standalone switch, desolder/disconnect and replace it.

5. 5

   Reassemble and Calibrate

   Reassemble the armrest. Reconnect the battery and power on the tractor. You must perform a tractor engine and armrest calibration procedure (often requiring the dealer diagnostic tool) to teach the ACML the new minimum and maximum voltage values of the replacement potentiometer.