Case IH 5118-11 - UCM – UCM: Vehicle controller communication fault with trailer brake controller

The tractor's main controller has lost the data link (typically via the CAN bus or J2497 Power Line Communications) with the electronic trailer brake control module. When this communication drops, the system cannot verify the trailer's brake configuration or send the necessary variable braking power signals to the trailer.

• MAGNUM AFS Connect
• Magnum
• Steiger
• Puma
• Farmall

1. 1

   Inspect the 7-way trailer plug for power supply issues, greenish corrosion, dirt, or loose pins that frequently disrupt communication signals.

2. 2

   Check the ground wire at the trailer plug and the controller to ensure a clean, solid connection.

3. 3

   Test the blue wire (brake actuation circuit) at the controller for hot voltage, and pierce the ground wire to ensure consistent grounding without electrical backfeed.

4. 4

   Verify the CAN bus data connections between the UCM and the trailer brake controller for pinched wires or rubbing that could cause a short to ground.

1. 1

   Clean Connections

   Disconnect the 7-way trailer plug and thoroughly clean all pins and connectors to remove any corrosion or debris.

2. 2

   Repair Wiring

   Trace the wiring harness from the rear plug to the trailer brake controller inside the cab. Repair any pinched, rubbed, or exposed wires that are grounding out the circuit.

3. 3

   Re-establish Ground

   Clean the grounding points for the trailer brake controller and ensure they are securely fastened to the chassis.

4. 4

   Replace the Controller

   If the wiring, plug, and grounds are all intact and testing shows proper voltage entering the controller but no communication output to the UCM, the internal circuitry of the trailer brake controller has failed and the module must be replaced.

5. 5

   Clear Codes

   After the repair, cycle the tractor's power and use a diagnostic tool to clear the inactive fault codes from the UCM / Pro monitor.