Case IH 518657-02 - UCM – UCM: Left brake switch disagreement

The control module is receiving conflicting or implausible signals from the left brake pedal switch, seeing both circuits as open or both as closed simultaneously. This points to a switch failure, a wiring short/break, or a misadjusted pedal.

• MAGNUM AFS Connect
• Magnum 400 AFS Connect
• Steiger AFS Connect

1. 1

   Physical Pedal Inspection: Verify that the left brake pedal returns fully to its resting position when released. Check for a sticky pedal pivot or broken return spring.

2. 2

   Visual Harness Check: Inspect the wiring harness and connector at the left brake switch (located under the cab console at the top of the pedal arm) for rubbed wires, corrosion inside the connector, or pushed-out pins.

3. 3

   Diagnostic Menu Monitoring: Access the tractor's onboard diagnostic display (via the AFS Pro monitor or the instrument cluster H-Menu) to monitor the live state of the left brake switch. Depress the pedal and watch for the state to change, flicker, or show an error state.

4. 4

   Multimeter Continuity Test: Unplug the switch and test the pins with a multimeter. When the switch plunger is extended vs. depressed, the NO and NC circuits should alternate continuity.

1. 1

   Preparation

   Park the tractor on a level surface, engage the parking brake, turn the ignition off, and disconnect the battery to prevent electrical spikes.

2. 2

   Access the Switch

   Remove the lower dash/steering console trim panels as necessary to gain clear access to the brake pedal linkages.

3. 3

   Removal

   Disconnect the electrical harness connector from the left brake switch. Loosen the retaining/lock nut holding the switch in its mounting bracket and unthread the switch.

4. 4

   Installation

   Thread the new brake switch into the mounting bracket.

5. 5

   Adjustment

   Adjust the switch depth so that the plunger is fully depressed by the pedal arm when the brake is released, but not bottomed out to the point of crushing the switch housing. Tighten the lock nut to secure the adjustment.

6. 6

   Reassembly

   Reconnect the electrical harness. Reinstall any removed trim panels.

7. 7

   Clearing Codes

   Reconnect the battery and turn the key to the ON position. Enter the diagnostic menu and clear the stored UCM fault codes.

8. 8

   Testing

   Depress the left brake pedal several times to ensure the brake lights illuminate correctly and verify that the 518657-02 fault code does not return.