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Home >> Lexus >> 2017 >> NX 200t Base, AWD >> Repair and Diagnosis (Single Page) >> Brakes >> Traction Control >> Vehicle Stability Control System- Diagnostics - Introduction >> Vehicle Stability Control System >> System Description [10/2014 - 05/2019] >> System Description [10/2014 - 05/2019]
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System Description [10/2014 - 05/2019]

  1. FUNCTION DESCRIPTION 
    1. ABS (Anti-lock Brake System)
      1. The ABS helps prevent the wheels from locking when the brakes are applied firmly or when braking on a slippery surface.
    2. EBD (Electronic Brake force Distribution)
      1. The EBD control utilizes ABS, and performs proper brake force distribution between the front and rear wheels in accordance with driving conditions. When braking while cornering, it also controls the brake forces of the right and left wheels, helping to maintain vehicle stability.
    3. BA (Brake Assist)
      1. The primary purpose of the brake assist system is to provide auxiliary brake force to assist the driver if the driver cannot generate a large enough brake force during emergency braking, thus helping to maximize the brake performance of the vehicle.
    4. TRAC (Traction Control)
      1. The TRAC system helps prevent the drive wheels from slipping when the driver depresses the accelerator pedal excessively when starting off or accelerating on a slippery surface.
    5. VSC (Vehicle Stability Control)
      1. The VSC system helps prevent the vehicle from slipping sideways as a result of strong front or rear wheel skid during cornering.
    6. Hill-start Assist Control
      1. When starting uphill, this control maintains the brake hydraulic pressure to the 4 wheels, in order to momentarily prevent the vehicle from descending backward.
    7. Brake Hold System
      1. The brake hold operation occurs when the brake pedal is depressed and the vehicle is fully stopped. Under brake hold, the wheel cylinder oil pressure of the 4 wheels is maintained, and the vehicle's fully stopped condition is sustained. When the acceleration pedal is depressed, the wheel cylinder oil pressure is automatically released. Also, depending on the vehicle conditions, the electric parking brake operates.
  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
    • The hydraulic circuit has 2 master cylinder cut solenoid valves, 4 pressure holding solenoid valves and 4 pressure reduction 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 the wheel cylinders.
    Skid Control ECU Motor Relay Supplies power to the pump motor.
    Solenoid Relay Supplies power to the solenoid valves.
    Speed Sensor Detects the wheel speed of each of the 4 wheels.
    Integration Control and Panel Assembly VSC OFF Switch Switches off the TRAC and VSC operation.
    Brake Hold Switch Permits the brake hold operation.
    Stop Light Switch Assembly Detects the brake pedal depressing signal.
    Stop Light Control ECU Assembly Illuminates the stop lights while brake hold control is operating.
    ECM
    • Sends the throttle position signal, accelerator pedal position signal and engine speed signal to the skid control ECU.
    • Controls the engine output based on the signals received from the skid control ECU.
    Parking Brake ECU Assembly
    • Sends the electric parking brake condition to the skid control ECU.
    • Controls the parking brake actuator assembly based on the signals received from the skid control ECU.
    Airbag ECU Assembly Yaw Rate and Acceleration Sensor
    • Detects the vehicle's yaw rate.
    • Detects the vehicle's acceleration in the forward, rearward and lateral directions.
    Steering 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 System Warning Light (Red Indicator)
    • Illuminates to alert the driver when the skid control ECU detects a malfunction in the EBD or brake system.
    • Illuminates to alert the driver when the brake fluid level is low.
    Multi-information Display (TRAC OFF Message) Illuminates to inform the driver when TRAC off mode is selected.
    VSC OFF Indicator Light Illuminates to inform the driver when VSC off mode is selected.
    Slip Indicator Light
    • Blinks to inform the driver when the TRAC or VSC system is performing control.
    • Illuminates to alert the driver when the skid control ECU detects a malfunction in the TRAC and/or VSC system.
    Brake Hold Standby Indicator Light Comes on when the system is in the brake hold control permission state.
    Brake Hold Operated Indicator Light
    • Comes on when the brake hold is operating.
    • Blinks when a malfunction has occurred during brake hold control selection.
    Brake Master Cylinder Sub-assembly Brake Fluid Level Warning Switch Detects the brake fluid level.