Principles of Operation

Auxiliary Brake System - Trailer Brake Control (TBC) Module

Principles of Operation

The Trailer Brake Control (TBC) module is an integrated electronic control device that is designed to provide variable braking power to the electric-actuated drum brakes on a towed trailer (1 to 4 axles only). The braking energy that is provided to the trailer is varied with a Pulse Width Modulated (PWM) voltage that switches between 0 volt and battery voltage, the higher the duty cycle the more braking power available.

The TBC module receives information from 2 different brake pedal inputs: a Brake Pedal Position (BPP) switch (also known as the stoplamp switch) and a brake pressure transducer. The BPP switch provides the PCM with current brake pedal position. This information is sent to the PCM as a voltage input and is then transmitted to the TBC module over the High Speed Controller Area Network (HS-CAN) bus. The brake pressure transducer provides a signal to the ABS module that varies with the force applied to the brake pedal. This information is also transmitted to the TBC module over the HS-CAN bus.

The TBC module also receives additional vehicle information over the HS-CAN bus. These inputs are from the PCM, the Instrument Cluster (IC) and the ABS module. These inputs are then used to determine the amount of braking power required for the trailer. The TBC module will also transmit information to the ABS module and the IC in regards to trailer connectivity and current TBC system status. System status information that is sent to the IC will be displayed in the IC message center to alert the driver of trailer status and any potential concerns.

TBC module output to the trailer can be adjusted by the driver through the use of the manual slide lever and the 2 gain buttons. Pressing a gain button with a trailer connected to the vehicle will adjust the TBC output to the trailer brakes to set the maximum assistance while making sure the trailer wheels do not lock while braking. The maximum setting is 10.0 and the minimum setting is 0.0. The manual control lever is used to manually apply the trailer brakes, independent of the vehicle brakes, in order to calibrate the trailer gain setting to the specific trailer loading and road conditions. For information on setting trailer gain, refer to the Owner's Literature.

The IC message center displays the trailer connectivity status as well as gain setting (number display) and relative trailer braking power (output bar graph) during a braking event. When a successful trailer connection is detected by the TBC module, the message center will display TRAILER CONNECTED. If the electrical connection to the trailer is lost or disconnected during the same ignition cycle, the message center will display TRAILER DISCONNECTED.

Trailer Brake Control (TBC) Module Start Up, Prove Out and Wake Up

The following information describes the normal operation of the TBC module during start up and prove out both with and without a trailer connected to the vehicle. When the ignition key is turned to the ON position, the message center in the IC will illuminate all LED segments (prove out) for approximately 3 seconds. At the same time, the TBC module will check for trailer connectivity, check the IC for trailer brake configuration and then display the appropriate message in the message center.

Start Up and Prove Out Without a Trailer Connected to the Vehicle

When the ignition key is turned to the ON position and the IC is configured for trailer brakes, after the message center proves out it will display TRAILER DISCONNECTED. Pressing a gain button or moving the manual sliding switch will cause the message center to display TBC GAIN = XX.X NO TRAILER. XX.X being the current gain setting in the TBC module.

When the ignition key is turned to the ON position and the IC is not configured for trailer brakes, after the message center proves out the TBC module will shut down and the system will be inoperative. Pressing the gain button or moving the manual sliding switch will cause TBC FAULT to be displayed in the message center and a DTC will be set in the TBC module. For information on programming the IC for trailer brakes, refer to Programmable Parameters.

Start Up and Prove Out With a Trailer Connected to the Vehicle

When the ignition key is turned to the ON position and the IC is configured for trailer brakes, after the message center proves out it will display TRAILER CONNECTED. Pressing a gain button or moving the manual sliding switch will cause the message center to display TBC GAIN = XX.X OUTPUT = //////. XX.X being the current gain setting in the TBC module and ////// being the current output to the trailer. One bar is the least amount of output, 6 bars is the maximum.

If the IC is not configured for trailer brakes, the TBC module will react the same as indicated above in Start Up and Prove Out Without a Trailer Connected to the Vehicle.

TBC Module Wake Up

With a trailer connected to the vehicle, the TBC module will remain active while the ignition key is in the ON position to monitor the vehicle and trailer brake systems. Without a trailer connected to the vehicle, the TBC module will enter a "sleep mode" but will continue to send a PWM voltage signal to the trailer tow connector every 4 seconds to detect when a trailer is connected.

When the ignition key is in the ON position and the module is in sleep mode, pressing a gain button or sliding the manual switch will cause the module to "wake up". If a trailer is not connected to the vehicle, the message center display should prove out for 3 seconds and then display TRAILER DISCONNECTED. If a trailer is connected to the vehicle, the display should prove out for 3 seconds and then display TRAILER CONNECTED.