Case IH 12958 – Vehicle Controller / MTA CCM or Instrument Cluster (ADIC): Trailer Brake Controller Communication Fault with Vehicle Controller

The Vehicle Controller is either not receiving the expected CAN bus messages from the Trailer Brake Controller (timeout) or the message counter for the Pneumatic Brake / Trailer Brake (PB_TBR_27) data packet has failed or fallen out of sync.

• MAXXUM T4E
• Case IH Farmall series
• Maxxum
• Puma

1. 1

   Check system voltage to verify the tractor is not experiencing undervoltage (e.g., during cranking) or overvoltage, which can cause CAN modules to drop offline.

2. 2

   Inspect CAN bus wiring between the Trailer Brake Controller and the Vehicle Controller for chafed wires, pinched harnesses, or loose pins in the connectors.

3. 3

   Check the 7-pin trailer connector at the rear of the tractor for corrosion, dirt, or a bad ground that could short the brake circuit.

4. 4

   Verify the trailer brake configuration is set correctly in the vehicle's display.

5. 5

   Check for the presence of fault code 12965, which indicates an internal Trailer Brake Controller fault.

1. 1

   Disconnect Power

   Always disconnect the negative battery cable before working on the tractor's CAN bus or electrical systems to prevent short circuits.

2. 2

   Clean and Reseat Connectors

   Locate the Trailer Brake Controller (typically mounted under the dash or integrated into the right-hand console depending on the model). Unplug the controller, spray the contacts with electrical contact cleaner, and securely reconnect it.

3. 3

   Repair Wiring

   If the diagnostic checks revealed damaged CAN-High or CAN-Low wires between the controller and the CCM, splice and repair the wiring using proper heat-shrink connectors.

4. 4

   Replace the Controller

   If the wiring is intact, the ground is good, and the controller still fails to communicate (or has an internal fault code), remove the mounting bracket hardware, unplug the custom wiring harness, and install a new Trailer Brake Controller.

5. 5

   Test the System

   Reconnect the negative battery cable. Turn the key to the ON position and clear the stored fault codes. Connect a trailer (or a trailer simulator tester) to verify that the brake controller is recognized and proportional braking power is being applied without triggering the 12958 code.