System Description

BRAKE CONTROL: VEHICLE STABILITY CONTROL SYSTEM (for Vacuum Brake Booster): SYSTEM DESCRIPTION

1. SYSTEM DESCRIPTION

HINT
The skid control ECU is built into the brake actuator.

(a) ABS (Anti-lock Brake System)

The ABS helps prevent the wheels from locking when the brakes are applied firmly or on a slippery surface.

(b) EBD (Electronic Brake Force Distribution)

The EBD control utilizes the ABS, performing proper brake force distribution between the front and rear wheels in accordance with the driving conditions. When the brakes are applied while cornering, it also controls the braking forces of the right and left wheels, helping to maintain vehicle stability.

(c) BA (Brake Assist)

The primary purpose of the brake assist system is to provide auxiliary brake force to assist drivers who cannot generate a brake force large enough during emergency braking, thus helping to maximize the vehicle's braking performance.

(d) TRAC (Traction Control) (for 2WD vehicles or 4WD vehicles in H2 or H4* mode)

The TRAC system helps prevent the drive wheels from slipping if the driver presses down on the accelerator pedal excessively when starting off or accelerating on a slippery surface.

*: In H4 mode, the system performs only brake control.

(e) VSC (Vehicle Stability Control) (for 2WD vehicles or 4WD vehicles in H2 or H4 mode)

The VSC system helps prevent the vehicle from slipping sideways when front or rear wheel skidding occurs while cornering.

(f) AUTO LSD (Auto Limited Slip Differential)

For 2WD vehicles and 4WD vehicles in H2 mode, the AUTO LSD will operate with the VSC OFF switch on (TRAC OFF mode (AUTO LSD control)) and the accelerator pedal depressed.

The AUTO LSD system is used to apply brake pressure and limit differential slippage, thus transmitting drive torque to the other drive wheel to ensure traction when starting under the following conditions:

* One of the drive wheels spins, for example, when one drive wheel is driven off of the pavement.

* One of the drive wheels slips on snow/ice when starting on a slope.

HINT
The AUTO LSD is temporarily disabled when the brake pedal is depressed.

2. ABS with EBD, BA, TRAC and VSC OPERATION

(a) The skid control ECU (brake actuator assembly) calculates vehicle stability tendency based on the signals from the 4 wheel speed sensors, the yaw rate and deceleration sensor, and the steering angle sensor. In addition, it evaluates the results of the calculations to determine whether any control actions (control of the engine output torque by electronic throttle control and of the brake fluid pressure by the brake actuator) should be implemented.

(b) The slip indicator blinks and the VSC warning buzzer sounds to inform the driver that the VSC system is operating. The slip indicator also blinks when traction control is operating, and the operation being performed is displayed.

3. INITIAL CHECK

(a) When the vehicle speed first reaches approximately 6 km/h (4 mph) or more after the ignition switch has been turned ON, each solenoid valve and the brake actuator motor are sequentially activated to perform electrical checks. During the initial check, the operating sound of the motor can be heard from the engine compartment, but this does not indicate a malfunction.

4. FUNCTION OF COMPONENTS