Case IH 18260 (518736.03, 518736.04) - ACML – Armrest Control Module (ACML / ARM): Front Hitch Drop Rate Potentiometer Error

The controller is detecting that the potentiometer's voltage signal is either too high (shorted to power) or too low (shorted to ground/open circuit), or that its calibration values are out of range. This prevents the operator from properly controlling the drop rate of the front hitch.

• MAXXUM T4E
• VESTRUM CVX
• Case IH Magnum Series (Magnum 235-340 Series 4, MX Magnum, 7200 series)
• Case IH Farmall Series (115U Pro EP)
• Case IH Vestrum

1. 1

   Visually inspect the armrest controller for damaged wires, loose connections, or bent pins.

2. 2

   Open the armrest controller housing and disconnect connector J2 of the second panel from the armrest controller.

3. 3

   Measure the continuity between pin 1 and pin 2 of connector J2. The resistance should be approximately 2k ohms.

4. 4

   Measure between pin 2 and pin 8 while turning the drop rate potentiometer. The resistance should change smoothly and continuously from roughly 0.1k ohms to 1.1k ohms (Note: On some older Magnum models, the specification is 10,000 ohms ± 10% across pins A to C).

5. 5

   Turn the tractor key switch to the ACC position and check the power supply coming from the armrest controller at pin 1 of J2. It should read approximately 8 volts.

1. 1

   Replace armrest controller

   If the power supply check at pin 1 of J2 does not yield ~8 volts, the armrest controller itself has failed and must be replaced.

2. 2

   Replace potentiometer or second panel

   If the potentiometer fails the resistance sweep test (dead spots, open circuit, or out of spec), replace the hitch drop rate potentiometer or the entire second panel of the armrest, depending on how the assembly is serviced for your specific model.

3. 3

   Clean connectors and reconnect

   If both the controller voltage and potentiometer resistance are good, thoroughly clean the connectors and reconnect the second panel to the armrest controller.

4. 4

   Recalibrate armrest controller

   Turn the key on and use the tractor's display/service tool to recalibrate the armrest controller (specifically the hitch drop rate potentiometer calibration).

5. 5

   Recheck fault codes

   Check the fault codes again. If the code does not return, the issue was a poor connection. If the code returns after passing all wiring tests, replace the armrest controller.