Case IH 12142 – VCU: CAN – VCU_TRAIL_BRAKE-INH error / not available

A Controller Area Network (CAN) communication error or an integrity check failure regarding the trailer brake inhibit flag. The system is failing to detect the switch connector or the activated data for the trailer brake inhibit function.

• Puma/Mid Range Magnum
• MAXXUM T4E
• Puma series
• Steiger
• Maxxum

1. 1

   Inspect connectors identified in the wiring schematics as X036 and X121 for the parking brake switch

2. 2

   Inspect the electronic parking brake relay identified as X012 and the parking brake connector X745

3. 3

   Check the CAN communication wiring harness leading to the VCU for open circuits, shorts to ground, or corrosion

4. 4

   Verify that the trailer brake inhibit data is being properly transmitted across the CAN bus when the parking brake is engaged

1. 1

   Access the Parking Brake Switch

   Locate the parking brake switch in the cab and disconnect its connectors (X036, X121). Inspect for pushed-out pins, corrosion, or physical damage.

2. 2

   Test the Relay

   Locate the electronic parking brake relay (X012) in the fuse/relay panel. Swap it with a known good relay of the same type to test for proper switching operation.

3. 3

   Check Harness Continuity

   Using a multimeter, verify the continuity of the wiring harness between the parking brake switch, the electronic parking brake relay, and the VCU. Repair any broken wires or shorts.

4. 4

   Replace Faulty Components

   If the wiring is intact but the switch or relay fails testing, replace the defective component.

5. 5

   Clear and Retest

   Reconnect all harnesses, turn the ignition key on, and use a diagnostic service tool to clear fault code 12142. Cycle the parking brake and test the trailer brake systems to ensure the CAN message is broadcasting correctly and the code does not return.