Reverse proximity sensors are used to determine an angle between a towed trailer and the towing vehicle. The trailer sway control determines a trailer angle of sway based upon proximity sensor readings from the reverse proximity sensors and from a sensor reading of an angle of turn of a steering wheel of the towing vehicle. Provided the determined trailer angle of sway exceeds a range that can be tolerated, a controller sends instructions to apply necessary braking to the vehicle or trailer to mitigate the trailer sway.