Case IH 518557-06 - ACM – ACM: EHR settings adjustment knob voltage low

The signal voltage returning from the EHR flow/timer adjustment potentiometer (knob) to the controller has dropped below the minimum acceptable threshold (typically below 0.5V on a 5V reference circuit). This condition is almost always caused by a short to ground in the signal wire, a severed/open wire, a loss of the 5V reference voltage, or an internal failure of the knob's potentiometer itself.

• MAGNUM AFS Connect
• Magnum Series
• Steiger / Quadtrac Series
• Puma Series
• Optum Series
• Maxxum Series

1. 1

   Visual Inspection: Remove the armrest cover and inspect the wiring harness leading to the EHR adjustment knob. Look for pinched wires, chafing against the plastic housing, or loose connector pins.

2. 2

   Voltage Check (Reference & Ground): Disconnect the knob. Turn the key to the ON position. Use a multimeter to verify that the connector is receiving a steady 5V reference signal from the ACM and has a solid ground.

3. 3

   Signal Wire Continuity: Test the signal wire between the knob's connector and the ACM harness plug. Ensure there is no continuity to ground (which would indicate a short to ground causing the voltage low code).

4. 4

   Potentiometer Sweep Test: If the wiring is intact, test the resistance of the knob itself while turning it. If the resistance drops to zero, shows an open circuit, or has erratic dead spots, the internal potentiometer has failed.

1. 1

   Prep the Machine

   Park the tractor on a level surface, turn off the engine, remove the key, and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Access the ACM Panel

   Remove the Torx/Phillips retaining screws securing the top cover of the main Multicontroller armrest panel.

3. 3

   Lift the Panel

   Carefully lift the armrest console cover. Do not pull forcefully, as the wiring harnesses for the EHR levers, PTO switches, and encoders are still attached.

4. 4

   Remove the Faulty Knob

   Locate the EHR settings adjustment knob on the underside of the panel. Disconnect its electrical pigtail. Remove the retaining nut or locking tabs securing the potentiometer to the plastic console and pull the knob out.

5. 5

   Install the New Part

   Insert the new EHR adjustment knob into the console, secure the retaining nut/clips, and plug the electrical connector back in.

6. 6

   Reassembly

   Carefully lower the armrest cover back into place, ensuring no wires are pinched, and reinstall the retaining screws.

7. 7

   Calibration

   Reconnect the battery and turn the key ON. Clear the stored fault codes via the AFS Pro display. Navigate to the EHR settings screen and verify that turning the knob smoothly adjusts the flow/timer settings on the display without triggering a new fault. (Note: Depending on the software version, a quick EHR lever/knob calibration via the HH menu may be required).