Case IH 603-04 - UCM – UCM: Abnormal voltage reading on the Top of brake switch left circuit

Indicates a circuit fault related to the left brake pedal switch, pointing to an abnormal voltage reading on the 'Top of brake switch left' circuit. This is typically a hard electrical fault such as a short to ground, a short to a voltage source, or a failed internal switch contact.

• MAGNUM AFS Connect

1. 1

   Inspect the left brake pedal assembly to ensure the pedal returns fully to its resting position and that the top brake switch is not physically stuck, broken, or misaligned.

2. 2

   Inspect the wiring harness connecting the left brake switch to the UCM for chafed wires, pinched harnesses under the dash console, or corroded connector pins.

3. 3

   Using a multimeter, check the signal wire at the brake switch connector for a short to ground or a short to power.

4. 4

   Connect the CNH Electronic Service Tool (EST), turn the ignition switch ON, and monitor the live status of the left brake switch while actuating the pedal manually to see if the UCM registers the state change.

1. 1

   Park the machine on a level surface, turn off the key switch, and disconnect the battery to prevent electrical damage.

2. 2

   Remove the lower dash or steering console panels as necessary to access the brake pedal assembly.

3. 3

   Locate the top switch on the left brake pedal and disconnect its electrical connector.

4. 4

   Test the switch for continuity.

   Actuate the switch manually; if it does not show proper continuity changes (opening and closing the circuit), the switch has failed internally and must be replaced.

5. 5

   If the switch tests good, trace the wiring harness back to the UCM.

   Repair any damaged, rubbed, or broken wires found in the circuit.

6. 6

   Install the new switch (or reconnect the existing one if repairing the harness) and ensure it is properly adjusted so that the pedal arm engages it correctly.

7. 7

   Reconnect the battery, turn the key switch ON, and use the EST or the in-cab AFS display to clear the inactive fault codes.

   Test the brake pedals to ensure the code does not return.