BRAKE CONTROL SYSTEM

FUNCTION OF MAIN COMPONENTS

Component		Function
Brake Actuator Assembly		Consists of 2 master cylinder cut solenoid valves, 4 pressure application solenoid valves, and 4 pressure reduction solenoid valves. The master cylinder pressure sensors, the accumulator pressure sensor, the wheel cylinder pressure sensors and the relief valve are installed in the brake actuator.
Brake Booster Pump Assembly	Accumulator	Stores the hydraulic pressure that was generated by the pump. The accumulator is filled with high pressure nitrogen gas.
Brake Booster Pump Assembly	Pump and Pump Motor	Draws up brake fluid from the reservoir tank and provides high hydraulic pressure to the accumulator.
Brake Master Cylinder Sub-assembly	Master Cylinder	Generates hydraulic pressure in accordance with the brake pedal depression force.
	Brake Stroke Simulator Cylinder Sub-assembly	Provides a pedal stroke during braking in accordance with the driver's pedal effort.
	Stroke Simulator Cut Valve	Allows fluid pressure generated by the brake master cylinder sub-assembly to flow into the brake stroke simulator cylinder sub-assembly while the electronically controlled brake system operates.
Brake Master Cylinder Reservoir Assembly	Brake Fluid Level Warning Switch	Detects a low brake fluid level.
Brake Control Power Supply with Bracket Assembly		An auxiliary power supply to provide stable electrical power to the brake system. When the voltage of the auxiliary battery is low, the brake control power supply with bracket assembly supplements the supply of power to the brake system by providing the electric charge that is stored in the unit.
Combination Meter Assembly	Brake Warning Light (Red Indicator)	Illuminates to alert the driver that the skid control ECU assembly detects the malfunction in the apportioning of the brake force. Illuminates to inform the driver when the brake fluid is low.
	Brake Warning Light (Yellow Indicator)	Illuminates to alert the driver that a minor malfunction which does not affect the braking force has occurred in the brake system.
	ABS Warning Light	Illuminates to alert the driver when the skid control ECU assembly detects a malfunction in the ABS, EBD or brake assist.
	Slip Indicator Light	Blinks to inform the driver when the TRC, VSC or ABS is operational. Illuminates to alert the driver when the skid control ECU assembly detects a malfunction in the TRC or VSC.
	VSC OFF Indicator Light	Illuminates to inform the driver when VSC OFF mode is selected.
	Brake Hold Operated Indicator Light	Illuminates to inform the driver that the brake hold function is operating. Blinks to alert the driver when the skid control ECU assembly detects a malfunction in the brake hold function.
	Brake Hold Standby Indicator Light	Illuminates to inform the driver that the brake hold standby condition has been established.
	Master Warning Light	Illuminates when the warning message is displayed in the multi-information display.
	Multi-information Display	Displays the information message when TRC OFF mode is selected. Displays the warning message when the skid control ECU assembly detects a malfunction in the system.
	Buzzer	Sounds together with a message display on the multi-information display during a system malfunction.
Stop Light Switch Assembly		Detects when the brake pedal is depressed.
Semiconductor PWR Integration ECU	Stop Light Control Relay	Illuminates or blinks the stop lights in accordance with signals received from the stop light switch assembly and skid control ECU assembly.
Brake Pedal Stroke Sensor Assembly		Directly detects the extent of the brake pedal stroke operated by the driver.
Combination Switch Assembly	VSC OFF Switch	Enables the driver to select "Normal Mode", "TRC OFF Mode", or "VSC OFF Mode".
Electric Parking Brake Switch Assembly	Brake Hold Switch	Switches the brake hold function on and off.
Front Door Courtesy Light Switch Assembly (Driver Side)		Detects whether the driver door is open or closed, sends the information to the skid control ECU assembly and activates the electrically controlled brake system when the door is opened while the power switch is off.
Speed Sensor		Detects the wheel speed of each of the 4 wheels.
Yawrate Sensor Assembly		Detects the vehicle's longitudinal and lateral acceleration. Detects the vehicle yaw rate.
Steering Sensor		Detects the direction and angle of the steering wheel.
ABS MTR1 and MTR2 Relay		By controlled by the skid control ECU assembly, supply power to the pump motor. Under the normal condition, the ABS MTR1 Relay is used. When a malfunction is detected in the ABS MTR1 Relay, the ABS MTR2 Relay is used instead.
Skid Control ECU Assembly		Monitors the driving conditions of the vehicle in accordance with the signals received from the sensors, and through cooperative control with each ECU, calculates the required amount of braking force, and controls the brake actuator assembly.
Power Steering ECU Assembly		Controls the steering assist torque based on the signals received from the skid control ECU assembly.
Hybrid Vehicle Control ECU Assembly		Actuates regenerative braking upon receiving a signal from the skid control ECU assembly. Sends the actual regenerative braking control value to the skid control ECU assembly. Controls the drive force based on an output control request signal received from the skid control ECU assembly while the VSC or TRC is operating.
Parking Brake ECU Assembly		Sends the electric parking brake condition to the skid control ECU assembly. Controls the parking brake actuator assembly based on the signals received from the skid control ECU assembly.
ECM Assembly		Performs engine output control based on the signal from the hybrid vehicle control ECU assembly.
Driving Support ECU Assembly*1		Sends brake request signals to the skid control ECU assembly.
Absorber Control ECU*2		Controls the absorber damping force based on signals received from the skid control ECU assembly when the VSC system is operating.
Network Gateway ECU		Relays data between buses.

*1: Models with pre-crash safety system

*2: Models with adaptive variable suspension system

SYSTEM CONTROL

Control	Function
Electronically Controlled Brake System	The electronically controlled brake system detects the amount that the brake pedal is depressed based on signals from the brake pedal stroke sensor assembly. The system uses the skid control ECU assembly to adjust the pressure supplied from the hydraulic pressure source for each wheel, generating optimal braking force.
Regenerative Braking Cooperative Control	This control performs cooperative control with regenerative braking that is specific to hybrid vehicles to efficiently charge the HV battery.
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 utilize the vehicle's braking performance.
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.
Trailer Sway Control (TSC)	If the tongue load is not properly adjusted while towing a trailer, trailer sway may be caused due to crosswinds, bumpy roads, steering operation, etc. Trailer sway control detects sway and regulates the brake of each wheel and the engine output in order to help to suppress trailer sway.
VSC and Cooperative Control with EPS1 or VSC+2	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 to the 4 wheels, in order to momentarily prevent the vehicle from descending backward.
Motive Force Control during TRC or VSC Operation	Transmits a motive force control signal from the skid control ECU assembly to the hybrid vehicle control ECU assembly to limit the motive force while the TRC or VSC is being activated.
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.
Emergency Brake Signal	In the case of emergency braking, the emergency brake signal flashes the stop lights to alert drivers in following vehicles.

*1: Models for general countries

*2: Models for Europe

FAIL-SAFE

If a malfunction occurs in the skid control ECU assembly, sensors or brake actuator assembly, the system continues effecting brake control by excluding the malfunctioning area and using only the areas that are operating normally.
If the regenerative brake becomes unusable due to a failure in communication with the hybrid vehicle control ECU assembly, the skid control ECU assembly uses the hydraulic brake force to control the entire braking force.

DIAGNOSIS

If the skid control ECU assembly detects a malfunction in the brake control system, the warning lights illuminate and a warning message is displayed on the multi-information display. At the same time, a Diagnostic Trouble Code (DTC) is stored in the memory of the skid control ECU assembly.
If the skid control ECU assembly detects a malfunction during a sensor signal check (test mode), it stores the DTCs in its memory.
For details of DTCs and the check function, refer to the Repair Manual.