Auxiliary Brake System - Trailer Brake Control (TBC) Module: Overview
WARNING: This page is about a different car, the 2017 Lincoln Navigator and 2017 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.
The trailer brake system uses an ECU called the TBC module to provide variable braking power to the electric-actuated drum brakes on a towed trailer (1 to 4 axles only). The braking energy provided to the trailer is modulated with a PWM signal which varies between 0 volt and battery voltage, the higher the duty cycle the more braking power available.