Case IH 18268 (518756.03, 518756.04) - ACML – ACML: Rear Hitch Drop Rate Potentiometer

The voltage signal or calibration value received from the Rear Hitch Drop Rate Potentiometer is outside the normal operating range (either too high, too low, or out of calibration limits), preventing the controller from accurately determining the operator's desired drop rate.

• MAXXUM T4E
• VESTRUM CVX
• Magnum 235-340 Series 4
• MX Magnum
• Puma 165
• Puma 180
• Puma 195
• Puma 210
• Puma 225
• Maxxum 135 Multicontroller

1. 1

   Visually inspect the armrest controller housing and wiring harness for damaged wires, loose connections, or bent pins at the connectors (e.g., connector J2).

2. 2

   Perform a potentiometer resistance test by disconnecting the panel connector and measuring continuity across the main pins (should be approximately 2k ohms, or 10k ohms ± 10% on older models).

3. 3

   Perform a sweep test by measuring the signal pin while slowly turning the drop rate potentiometer dial to ensure resistance changes smoothly without dropouts.

4. 4

   Check the power supply reference voltage coming from the armrest controller to the potentiometer with the key in the ACC position (should read approximately 8V or 5V).

1. 1

   Turn off the tractor and ensure the key is removed.

2. 2

   Open the armrest console to access the internal wiring and the secondary control panel where the drop rate potentiometer is housed.

3. 3

   Replace the potentiometer or the secondary armrest panel assembly.

   Perform this if the diagnostic tests revealed a faulty potentiometer (open circuit, short, or erratic sweep).

4. 4

   Repair the affected wires or replace the harness section.

   Perform this if the wiring harness is damaged.

5. 5

   Replace the Armrest Control Module (ACML).

   Perform this if the potentiometer and wiring tested perfectly but the ACML is not sending the correct reference voltage.

6. 6

   Reconnect all harnesses, clean the connectors, and reassemble the armrest.

7. 7

   Calibrate the armrest controller and the hitch drop rate potentiometer.

   Turn the key on and use the tractor's display or an electronic service tool to perform the calibration.

8. 8

   Clear the fault codes and verify that the rear hitch lowers at the commanded rate without triggering the error.