System Description

WARNING: This page is about a different car, the 2008 Toyota Yaris. However, it is still accessible from the selected car via links, so may be relevant.

SYSTEM DESCRIPTION
HINT:

The skid control ECU forms a single unit with the brake actuator.
1. ABS (Anti-lock Brake System)
  The ABS helps prevent the wheels from locking when the brakes are applied firmly or on a slippery surface.
  
  Fig 1: Anti-Lock Brake System Communication Diagram
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  1. Operation description
    The skid control ECU detects wheel lock conditions by receiving vehicle speed signals from each speed sensor, and sends control signals to the pump motor and solenoid valve to prevent the wheels from locking by controlling the brake fluid pressure of each wheel cylinder. The ABS warning light comes on when the ABS system malfunctions.
2. EBD (Electronic Brake force Distribution)
  The EBD control utilizes the ABS, realizing the proper brake force distribution between the front and rear wheels in accordance with the driving conditions and vehicle load. In addition, when the brakes are applied while cornering, it also controls the braking forces of the right and left wheels, helping to maintain vehicle stability.
  
  Fig 2: Electronic Brake Force Distribution Communication Diagram
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  1. Operation description
    The skid control ECU receives speed signals from each speed sensor to detect the slip conditions of the wheels and sends control signals to the solenoid.
    
    The solenoid valve controls the brake fluid pressure of each wheel cylinder and divides the control power properly between the front and rear wheels and the right and left wheels. The BRAKE warning light comes on to indicate malfunctions in the EBD system.
ABS with EBD OPERATION
1. Based on the signals received from each of the 4 wheel speed sensors, the skid control ECU calculates the speed and deceleration of each wheel, and checks the wheel slippage conditions. The ECU controls the pressure holding valve and pressure reduction valve in order to adjust the brake fluid pressure of each wheel cylinder in accordance with the slippage conditions.
FAIL SAFE FUNCTION
1. When a failure occurs in the ABS system, the ABS warning light comes on and its operation is prohibited. In addition to this, when a failure which disables the EBD operation occurs, the brake warning light comes on and its operation is prohibited.
  If control is prohibited due to a malfunction during operation, control is disabled gradually to avoid sudden vehicle instability.
INITIAL CHECK
1. When the vehicle speed first reaches approximately 4 mph (6 km/h) or more after the ignition switch is turned to ON, each solenoid valve and the motor of the brake actuator are sequentially activated to perform electrical checks. During the initial check, the operating sound of the solenoid valve and motor can be heard from the engine compartment, but this does not indicate a malfunction.

FUNCTION OF COMPONENTS

FUNCTION COMPONENTS CHART

Components	Functions
Front speed sensor (Semiconductor speed sensor, magnetic sensor rotor)	Detects the wheel speed and sends a signal to the skid control ECU. The front speed sensor (semiconductor speed sensor) with the integrated bearing and the sensor rotor (magnetic sensor rotor) are installed on the front axle hub. The magnetic sensor rotor is equipped with north and south poles (48 of each), which are evenly spaced around its circumference. The magnetic field changes as the magnetic sensor rotor rotates. The semiconductor speed sensor detects the change and outputs it as the vehicle speed pulse.
Skid control sensor (Semiconductor speed sensor, magnetic sensor rotor)	The skid control sensor (semiconductor speed sensor) and the sensor rotor (magnetic sensor rotor) are installed on the rear axle carrier. The skid control sensor has the same structure and functions as the front speed sensor.
Skid control ECU (Housed in brake actuator)	Processes the signals from the sensors to control the ABS. Sends and receives control signals to and from the ECM via CAN communication.
Brake actuator	Consists of the master cylinder cut solenoid valve, holding solenoid valve, pump motor, and reservoir, and adjusts the brake fluid pressure applied to each wheel cylinder. Houses the skid control ECU.
Solenoid relay	Supplies power to each solenoid. Housed in the skid control ECU.
ABS warning light	Illuminates to inform the driver that a malfunction in the ABS has occurred. Blinks to indicate DTCs that relate to the ABS.
BRAKE warning light	Illuminates to inform the driver that the parking brake is ON when the system is normal, and when the brake fluid has decreased. Illuminates to inform the driver that a malfunction in the EBD has occurred.