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Home >> Lexus >> 2017 >> IS 200t Base >> Repair and Diagnosis >> Brakes >> Traction Control >> Vehicle Stability Control System - Diagnostics - Introduction (1 Of 3) >> Vehicle Stability Control System >> System Description [10/2016 - 09/2020] >> System Description [10/2016 - 09/2020]
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System Description [10/2016 - 09/2020]

  1. FUNCTION DESCRIPTION 
    1. Anti-lock Brake System (ABS)
      1. The ABS helps prevent the wheels from locking when the brakes are applied firmly or when braking on a slippery surface.
    2. Electronic Brake Force Distribution (EBD)
      1. 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 forces of the right and left wheels, helping maintain vehicle behavior.
    3. Brake Assist (BA)
      1. 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.
      2. 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.
    4. Traction Control (TRAC)
      1. The TRAC 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.
    5. Vehicle Stability Control (VSC)
      1. 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.
    6. Enhanced-VSC
      1. The Enhanced-VSC performs cooperative control with the power steering ECU assembly in order to provide steering assist in accordance with the operating conditions of the vehicle.
    7. Hill-start Assist Control
      1. When starting uphill, this control maintains the brake hydraulic pressure on all 4 wheels, in order to momentarily prevent the vehicle from descending backward.
  2. FUNCTION OF COMPONENTS 
    Component Function
    Brake Actuator Assembly Skid Control ECU Judges the vehicle driving condition based on the signals from each sensor, and sends the brake control signals to the brake actuator assembly.
    Master Cylinder Pressure Sensor Assembled in the brake actuator assembly, detects the master cylinder pressure.
    Pump Motor Drives the pumps inside the brake actuator assembly.
    Solenoid Valves 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.
    Skid Control ECU ABS Motor Relay Supplies power to the pump motor.
    ABS Solenoid Relay Supplies power to the solenoid valves.
    Speed Sensor Detects the wheel speed of each of the 4 wheels.
    Combination Switch Assembly VSC OFF Switch Enables the driver to select the Normal mode, TRAC off Mode, or VSC off mode.
    Stop Light Switch Assembly Detects the brake pedal depressing signal.
    Main Body ECU (Multiplex Network Body ECU) Transmits the parking brake switch signal to the skid control ECU.
    Parking Brake Switch Assembly Detects the parking brake pedal status.
    ECM
    • Sends the throttle position signal, accelerator pedal 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.
    Yaw Rate and Acceleration Sensor
    • Detects the vehicle's longitudinal and lateral acceleration.
    • Detects the vehicle's yaw rate.
    Steering Angle Sensor Detects the steering direction and angle of the steering wheel.
    Combination Meter Assembly ABS Warning Light Illuminates to alert the driver when the skid control ECU detects a malfunction in the ABS.
    Brake Warning Light
    • Illuminates to alert the driver when the skid control ECU detects a malfunction in the EBD.
    • Illuminates to alert the driver when the brake fluid level is low.
    VSC OFF Indicator Light Illuminates to inform when driver of VSC off mode is selected.
    Slip Indicator Light
    • Blinks to inform the driver when the TRAC and VSC are operational.
    • Illuminates to alert the driver when the skid control ECU detects a malfunction in the TRAC or VSC.
    Multi-information Display
    • Displays an information message when TRAC OFF mode is selected.
    • Displays a warning message when the skid control ECU detects a malfunction in the ABS or EBD.
    Brake Master Cylinder Reservoir Assembly Brake Fluid Level Warning Switch Detects the brake fluid level.
    Brake Pedal Support Assembly Brake Pedal Load Sensing Switch Detects the brake pedal load.
    Semiconductor PWR Integration ECU Illuminates or flashes the stop lights in accordance with the signals from the stop light switch assembly and skid control ECU.
    Power Steering ECU Assembly Controls the steering assist torque based on the signals received from the skid control ECU.
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