APPARATUS AND METHOD FOR TRAILER SERVICE BRAKE CONTROL

A system on a tractor for controlling trailer service brakes comprises a manually operated trailer brake switch, a first electropneumatic valve in communication with a pressure source and a controller. The controller has an input communicating with the trailer brake switch, an output communicating with the electropneumatic valve and control logic. The control logic receives an input from the trailer brake switch indicating a driver's request to apply the trailer service brakes of the combination vehicle, determines if a predetermined condition exists and transmits a signal to the output to the electropneumatic valve. The electropneumatic valve transmits pressure to a trailer service control line to actuate the trailer service brakes in response to the trailer brake switch and existence of the predetermined condition.