BRAKE CONTROL SYSTEM

FUNCTION OF MAIN COMPONENTS

Component		Function
Speed Sensor		Detect the wheel speed of each of the 4 wheels.
Yawrate Sensor		Detects the vehicle's longitudinal and lateral acceleration. Detects the vehicle's yaw rate.
Roll Rate and Vertical Acceleration Sensor (Yawrate Sensor)		Detects the vehicle's vertical acceleration.
Spiral Cable with Sensor Sub-assembly	Steering Angle Sensor	Detects the direction and angle of the steering wheel.
Stop Light Switch Assembly		Detects when the brake pedal is depressed.
Brake Pedal Support Assembly	Brake Pedal Load Sensing Switch	Detects the brake pedal load.
Pad Wear Indicator Wire Assembly		Detects the amount of wear on the brake pads.
Brake Master Cylinder Reservoir Assembly	Brake Fluid Level Warning Switch	Detects the brake fluid level.
Integration Control and Panel Assembly	VSC OFF Switch	Enables the driver to select "Normal Mode", "TRC OFF Mode", or "VSC OFF Mode".
Brake Hold Switch		Switches the brake hold on and off.
Combination Switch Assembly	Drive Mode Select	Selects expert mode in combination with VSC OFF switch operation.
Brake Actuator Assembly	Skid Control ECU	Judges the vehicle driving condition based on the signals from each ECU, sensor and switch, and sends the brake control signals to the brake actuator. Based on signals from various sensors, outputs the emergency brake signal control signals.
	Solenoid Relay	Supplies power to the solenoid valves.
	Motor Relay	Supplies power to the pump motor.
	Motor Cut Relay	Cuts the power to the pump motor when the motor relay malfunctions.
	Master Cylinder Cut Solenoid Valve	Change the fluid path based on the signals from the skid control ECU during the operation of the brake control system functions in order to control the fluid pressure applied to each wheel cylinder.
	Pressure Holding Solenoid Valve
	Pressure Reduction Solenoid Valve
	Pump Motor	Drives the pumps inside the brake actuator.
	Master Cylinder Pressure Sensor	Built into the brake actuator, detects the master cylinder pressure.
Parking Brake ECU Assembly		Controls the electric parking brake system.
ECM		Sends the throttle position signal, accelerator pedal position signal, shift position signal, engine speed signal etc., to the skid control ECU. Controls the engine output based on the signals received from the skid control ECU. Sends the brake control request signal from the dynamic radar cruise control system to the skid control ECU.*
Power Steering ECU Assembly		Controls the steering assist torque based on the signals received from the skid control ECU.
Combination Meter Assembly	Brake Warning Light /Red (Malfunction)	Each of the lights and buzzers inform the driver of system operations, malfunctions, or control restriction conditions. Also, messages are displayed on the multi-information display in response to system abnormalities and system malfunctions.
	Brake Warning Light /Yellow (Minor Malfunction)
	ABS Warning Light
	TRC OFF Indicator Light
	VSC OFF Indicator Light
	Slip Indicator Light
	Parking Brake Warning Light
	Brake Hold Indicator Light (Green Indicator)
	Brake Hold Indicator Light (Yellow Indicator)
	Master Warning Light
	Multi-information Display
	Buzzer
Driving Support ECU Assembly*		Sends the brake control request signal from the pre-crash safety system to the skid control ECU.
Network Gateway ECU		Relays and transmits each CAN communication data signal.
Absorber Control ECU		Controls the damping force based on the signals received from the skid control ECU.
Main Body ECU (Multiplex Network Body ECU)		Sends a driver door open or closed condition signal to the skid control ECU assembly.
Airbag ECU Assembly		Sends the seat belt fasten condition signal to the skid control ECU assembly.
No. 2 Engine Room Relay Block	No. 2 Integration Relay	Illuminates the stop lights in accordance with the signals from the stop light switch assembly and skid control ECU.

*: Models with Lexus Safety System +

SYSTEM CONTROL

The brake control system has the following system/functions:

Control	Function
Anti-lock Brake System (ABS)	The ABS helps prevent the wheels from locking when the brakes are applied firmly or when braking on a slippery surface.
Electronic Brake Force Distribution (EBD)	The EBD utilizes ABS, achieving proper brake force distribution between the front and rear wheels in accordance with the driving conditions. In addition, during braking while cornering, the EBD also controls the brake force of the right and left wheels, helping maintain vehicle stability.
Brake Assist	The primary purpose of brake assist is to provide an auxiliary brake force to assist a driver who cannot generate a large brake force during emergency braking, thus helping ensure the vehicle's braking performance. If the brake booster malfunctions and the skid control ECU judges that the brake pedal force applied by the driver is not sufficient to ensure adequate braking force, brake assist is used to enhance the braking force.
Traction Control (TRC)	The TRC helps restrain the slippage of the drive wheels if the driver depresses the accelerator pedal excessively when starting off or while accelerating on a slippery surface.
Vehicle Stability Control (VSC)	The VSC helps restrain sideways slippage of the vehicle during a strong front wheel skid or strong rear wheel skid, which may occur while cornering.
Steering Cooperative Control	Effects cooperative control with the power steering ECU assembly in order to provide steering assist in accordance with the operating conditions of the vehicle.
Hill-start Assist Control	When starting uphill, this control maintains the brake hydraulic pressure on all 4 wheels, in order to momentarily prevent the vehicle from descending backward.
Brake Hold	As the driver depresses the brake pedal and the vehicle comes to a stop, this function maintains the hydraulic pressure of the 4 wheels in order to keep the vehicle stopped.
Radar Cruise Control Brake*	When the driving support ECU assembly determines that a large amount of deceleration is required based on the distance to the preceding vehicle and the relative vehicle speed during the dynamic radar cruise control system operation, the skid control ECU operates the brake system according to the signal from the ECM.
Pre-crash Brake*	When the driving support ECU assembly determines that the possibility of a collision is high or an unavoidable collision condition exists, the skid control ECU activates the pre-crash brake assist or the pre-crash brake according to the signal from the driving support ECU assembly.
Emergency Brake Signal	In the case of emergency braking, the emergency brake signal flashes the stop lights to alert drivers in following vehicles.

*: Models with Lexus Safety System +

FAIL-SAFE

If a malfunction occurs in the skid control ECU, sensors or brake actuator assembly, the system continues performing brake control by excluding the malfunctioning area and using only the areas that are operating normally.

DIAGNOSIS

If the skid control ECU detects a malfunction in the brake control system, the warning lights or indicator light illuminate. At the same time, a Diagnostic Trouble Code (DTC) is stored in the memory of the skid control ECU.
This system has a sensor signal check (test mode) function.
For details of DTC and check function, refer to the Repair Manual.