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 know 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 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 TBC module faceplate displays the trailer connectivity status (blue trailer icon) 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 blue trailer icon will illuminate solidly. If the electrical connection to the trailer is lost or disconnected, the trailer icon will flash. If the connection is lost while the vehicle is stationary, the indicator will turn off 30 seconds after sliding the manual switch or pressing a gain button. Sliding the manual switch or pressing a gain button after the icon turns off will cause the icon to illuminate and flash for an additional 30 seconds. If the connection is lost while the vehicle is moving, the trailer icon will flash until the ignition switch is turned to the OFF position or until the connection is reestablished. The TBC module will also send the TRAILER DISCONNECTED message to the IC message center.

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 is turned to the RUN position, the TBC module display will illuminate the vacuum fluorescent display for approximately 3 seconds. At the same time, the TBC module will check for trailer connectivity and check the IC for trailer brake configuration.

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

If the IC is configured for trailer brakes, the vacuum fluorescent display will shut off after proving out and the message center in the IC will display TRAILER DISCONNECTED. Pressing a gain button will cause the gain setting display and the blue trailer icon to illuminate and flash for 5 seconds after releasing the gain button. Sliding the manual switch will cause the gain setting, output bar graph and the blue trailer icon to illuminate and flash for 5 seconds after the switch is released. Pressing a gain button or sliding the manual switch while the display is flashing will prolong the flashing for an additional 5 seconds.

If the IC is not configured for trailer brakes, the TBC module will shut down after the display proves out and the system will be inoperative. Pressing the gain button or sliding the manual switch will get no reaction from the TBC module. TBC FAULT will be displayed in the IC message center and a DTC will be set. For information on programming the IC for trailer brakes, refer to Programmable Parameters. Programming and Relearning

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

If the IC is configured for trailer brakes, after the vacuum fluorescent display proves out, the blue trailer icon will illuminate solidly indicating trailer connectivity. Pressing a gain button will cause the gain setting display to illuminate, a second press of the gain button will be needed to input a gain setting. Sliding the manual switch will cause the output bar graph to illuminate and display brake output to the trailer.

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 is activated and monitoring 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 RUN 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 display should prove out for 3 seconds, then the blue trailer icon should flash and the IC message center should display TRAILER DISCONNECTED. If a trailer is connected to the vehicle, the display should prove out for 3 seconds, then the blue trailer icon should illuminate solidly.