Circuit/System Description
The TCC Brake Switch signal hard wired to the TBCM is normally open and closes to battery voltage when the brake pedal is applied. A separate brake switch signal is hard wired to the Body Control Module (BCM) that is normally closed to battery voltage and opens when the brake pedal is applied. The BCM sends its brake switch information to the TBCM over GMLAN serial data. The TBCM compares the states of the two brake switch signals after a Master Cylinder Brake Pressure threshold is exceeded. If the brake switch signal states are not in agreement or if the serial data brake state is not valid, a DTC will set and the ITBC 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 system voltage (ignition voltage) to make sure that the voltage stays within the proper range. Damage to components, and incorrect data input can occur when the voltage is out of range. The TBCM monitors the system voltage over an extended length of time. If the TBCM detects a system voltage outside an expected range, DTC C0800 will set.
The trailer brake control module (TBCM) checks whether there is an ignition ground short fault. This diagnostic compares ignition state with the engine running state received over serial data to determine whether or not there is an ignition ground short fault.
The TBCM runs this diagnostics to check whether there is a fault on the internal TBCM 5 volt references used to monitor the SSR Control and Trailer Feedback circuits. This diagnostics checks if the circuits 5-volt references is within a range for normal operation.
The TBCM runs this diagnostics to check whether there is a fault on the internal TBCM 5-volt references used to monitor the User Gain switch circuits. This diagnostics checks if the circuits 5-volt references is within a range for normal operation.
The TBCM runs this diagnostics to check whether there is a fault on the internal TBCM 5 volt references used to monitor the Manual Apply switch circuits. This diagnostics checks if the circuits 5-volt references is within a range for normal operation.
The trailer brake control module (TBCM) diagnostic monitor detects faults on the solid state relay (SSR) relay control active low circuit.
The trailer brake relay control circuit high SSR enable circuit short to battery monitors for short-to-high faults on the trailer brake solid state relay (SSR) enable circuit. In general, the SSR enable short-to-high circuit diagnostic is executed whenever the SSR has been disabled for a minimum duration. Typically, the diagnosis is executed at TBCM power up. The diagnosis test passes, if TBCM detected the status is correct for consecutive 16 samples.
The trailer brake control module (TBCM) monitors for faults on the trailer brake solid state relay (SSR) output auxiliary supply voltage circuit for fault for a short to ground, short to battery, or open circuit.
The manual apply switch rationality diagnostic monitors for circuit rationality faults on the manual apply switch input. The manual apply switch consists of a primary circuit, which is used as the basis for determining the trailer brake manual apply gain, and a redundant circuit that is used to rationalize performance of the primary circuit.
Manual Trailer Brake Apply Request Switch Signal Invalid" diagnostic monitors for a manual apply switch that is stuck in an applied position.
Manual Trailer Brake Apply Request Switch Signal -plausibility failure diagnostic monitors for circuit rationality faults on the manual apply switch input. The manual apply switch consists of a primary circuit, which is used as the basis for determining the trailer brake manual apply gain, and a redundant circuit that is used to rationalize performance of the primary circuit. The manual apply switch position fault is detected when the absolute value of the difference between the primary manual apply switch input and redundant inputs exceeds a threshold for a certain amount of time.
The primary manual apply switch circuit diagnostic monitors for circuit faults on the primary manual apply switch input to the trailer brake control module (TBCM).
This DTC will also be set as current DTC when a fault is detected in 5-volt reference voltage or in TBCM ground circuit.
The redundant manual apply switch circuit diagnostic monitors for circuit faults on the redundant manual apply switch input to the trailer brake control module (TBCM).
This DTC will also be detected when a fault is detected in the 5-volt reference voltage or in TBCM ground circuit
The User Gain Switch consists of 2 control buttons-Gain Up, and Gain Down. The output signal from the trailer brake controller switch is connected, and monitored by trailer brake control module (TBCM).
The TBCM monitors the circuit fault for User Gain Switch input for faults that includes short to GND, short to battery, and open circuit. This DTC will also be reported when fault is detected in TBCM ground circuit.
The TBCM also monitors the input signal validity from the User Gain Switch.
The trailer brake control module diagnostic monitor detects faults on the solid state relay (SSR) driver module feedback circuit.
Trailer Brake Controls Description and Operation
This vehicle may be equipped with a trailer brake control (TBCM) system for electric trailer brakes. The power output to the trailer brakes is based on the amount of brake pressure being applied in the vehicles brake system. The available power output to the trailer brakes can be adjusted to a wide range of trailering situations.
| IMPORTANT | Connecting a trailer that is not compatible with the ITBC system may result in reduced or complete loss of trailer braking. There may be an increase in stopping distance or trailer instability which could result in personal injury or damage to your vehicle, trailer, or other property. An aftermarket controller may be available for use with trailers with surge, air or electric-over-hydraulic trailer brake systems. To determine the type of brakes on your trailer and the availability of controllers, check with your trailer manufacturer or dealer. |
| IMPORTANT | If your vehicle is equipped with an ITBC, the blunt cuts exist, but are not connected further in the harness. If you install an aftermarket trailer brake controller, the ITBC must be disconnected. Do not power both ITBC and aftermarket controllers to control the trailer brakes at the same time. |
The vehicle is equipped with the following trailer braking components
- Manual Trailer Brake Apply
- Trailer Gain Adjustment
- Trailer Brake Control Panel
- Trailer Brake DIC Display