Case IH 12835 – Trailer Brake Controller: Failure detection 'Interruption/LowCurrent' at internal backup valve (BUV)

The control module has detected an open circuit, a broken wire, or a current draw that is below the minimum expected threshold on the circuit controlling the internal backup valve (BUV) solenoid.

• MAXXUM T4E
• Stage V MR
• Farmall 115U
• Farmall 40-45-50 CVT
• Maxxum
• Puma
• Optum

1. 1

   Locate the Trailer Brake Valve block and inspect the wiring harness leading to the Internal Backup Valve (BUV) solenoid for chafing, breaks, or rodent damage.

2. 2

   Disconnect the harness at the BUV solenoid and check for moisture, corrosion, or backed-out pins.

3. 3

   Using a multimeter, measure the resistance across the pins of the BUV solenoid. An 'OL' (Open Loop) or infinite resistance reading confirms the solenoid coil has failed internally.

4. 4

   Check the continuity of the power and ground wires from the Trailer Brake Controller/CCM to the valve connector to rule out a broken wire in the main harness.

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the negative battery terminal.

2. 2

   Wiring Repair

   If the diagnostic checks reveal a broken wire or corroded connector, splice in a new pigtail connector or repair the wire using weather-sealed heat shrink connectors.

3. 3

   Valve/Solenoid Replacement

   If the BUV solenoid coil is open (failed resistance test): Clean the area around the Trailer Brake Valve to prevent dirt from entering the hydraulic/pneumatic system. Remove the retaining nut or bolts holding the BUV solenoid to the valve block. Install the new solenoid (or the complete Trailer Brake Valve assembly if the solenoid is not serviced separately).

4. 4

   Reassembly & Testing

   Reconnect the wiring harness and the battery. Turn the key on, clear the inactive fault codes via the diagnostic menu, and actuate the trailer brakes to verify the code does not return.