Circuit/System Description
The brake switch is hard wired to the trailer brake control module (TBCM). The body control module (BCM) sends a brake switch status serial data message to the TBCM. The TBCM compares the states of the brake switch signal to the serial data message after a master cylinder brake pressure sensor threshold is exceeded. If the brake switch signal and the serial data message are not in agreement or if the serial data message is not valid, a DTC will set and the trailer brake control system will be disabled.
Diagnostics are used to determine whether or not there is a fault with the brake pressure or wheel speed data being received by the TBCM over GMLAN serial data.
The loss of serial data brake pressure diagnostic is to determine whether or not there is a fault with the brake pressure data being received over GMLAN. This diagnostic looks at the brake pressure signal validity and protection value signals over a period of time to determine the fault state of the brake pressure sensor.
The loss of serial data wheel speed diagnostic is to determine whether or not there is a fault with the wheel speed data being received over GMLAN. This diagnostic looks at the wheel speed signal validity and sequence number errors over a period of time to determine the fault state
This diagnostic applies to internal microprocessor integrity conditions within the trailer brake control module (TBCM). This diagnostic also addresses if the TBCM is not programmed.
The trailer brake control module (TBCM) monitors the battery voltage. Damage to components, and incorrect data input can occur when the voltage is out of range.
The trailer brake control module (TBCM) monitors the ignition circuit. This diagnostic compares ignition state with the engine running state received over serial data to determine if there is an ignition circuit fault.
The trailer brake control relay receives inputs from the trailer brake control module (TBCM), these inputs are used to determine the amount of voltage the relay will supply to the trailer brakes.
The trailer brake control system (TBCM) has a control panel with the trailer gain and manual apply switches, which is located on the instrument panel to the left of the steering column. The control panel and switches allows you to adjust the amount of output, referred to as trailer gain, available to the electric trailer brakes and allows you to manually apply the trailer brakes. The Trailer Brake Control Panel, and switches is used along with the Trailer Brake Display Page on the driver information center to adjust and display power output to the trailer brakes.