Case IH 28 – Hitch / Electronic Draft Control (EDC) Module: Lift Arm Position Sensing Control Voltage High (Damaged Potentiometer Or Short To +12 Volts)

The controller is receiving a voltage signal from the rear rockshaft/lift arm position sensor that exceeds the normal operating limit (typically above the 5.0V reference limit). This indicates either an internally shorted potentiometer or a wiring harness short to a 12-volt power source.

• Magnum
• MXM
• Case IH MXM Series
• Case IH Puma Series
• Case IH MX Series
• Case IH CX Series
• Case IH JX Series
• Case IH Farmall Series
• Case IH CS Series
• Case IH CVX Series
• Case IH MXU Series

1. 1

   Visual Inspection: Inspect the lift arm position sensor (located on the rear rockshaft/lift arm assembly) and its linkage. Look for physical damage to the rotary drive element.

2. 2

   Connector Check: Disconnect the sensor's 3-pin weather-proof connector. Check for water ingress, corrosion, or bent pins.

3. 3

   Harness Short Test: With the key ON and the sensor disconnected, use a multimeter to check the signal wire on the tractor-side harness. If it reads +12 Volts, the wiring harness is shorted to battery voltage somewhere between the sensor and the EDC controller.

4. 4

   Sensor Drop Test: If you disconnect the sensor and the active fault code changes from Code 28 (Voltage High) to Code 27 (Voltage Low / Open Circuit), the wiring harness is likely intact, and the potentiometer itself has failed internally.

1. 1

   Preparation

   Lower the 3-point hitch completely to the ground to remove hydraulic pressure and mechanical tension. Turn off the tractor and remove the key.

2. 2

   Removal

   Locate the lift arm position sensor on the rear lift arm shaft. Disconnect the electrical harness.

3. 3

   Unlink

   Remove the retaining hardware holding the sensor linkage/drive rod (e.g., sensor lever or connecting rod) to the rockshaft.

4. 4

   Dismount

   Unbolt the potentiometer housing from its mounting bracket.

5. 5

   Installation

   Mount the new rotary potentiometer. Reattach the mechanical linkage, ensuring the sensor's rotary wiper is positioned in its neutral/center travel range so it is not physically maxed out when the arms move.

6. 6

   Reconnection

   Plug in the 3-pin electrical connector.

7. 7

   EDC Calibration

   Perform a Hydraulic Lift Calibration (often accessed via the tractor's H-Menu or via an EST diagnostic tool). This teaches the EDC controller the new minimum (fully lowered) and maximum (fully raised) voltage values of the new sensor.