System Description

SYSTEM DESCRIPTION
HINT:

The skid control ECU forms a single unit with the hydraulic brake booster.
1. ABS (Anti-lock Brake System)
  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)
  The EBD control utilizes ABS, realizing proper brake force distribution between the front and rear wheels in accordance with the driving conditions and vehicle load.
  
  In addition, when braking while cornering, it also controls the brake forces of the right and left wheels, helping to maintain the vehicle performance.
3. BA (Brake Assist)
  The primary purpose of the brake assist system is to provide an auxiliary brake force to assist drivers who cannot generate a large enough brake force during emergency braking, thus helping to maximize the vehicle's brake performance.
4. VSC (Vehicle Stability Control)
  The VSC system helps prevent the vehicle from slipping sideways as a result of strong front wheel skid or strong rear wheel skid during cornering.
5. TRAC (Traction Control)
  The TRAC system helps prevent the drive wheels from slipping if the driver presses down on the accelerator pedal excessively when starting or accelerating on a slippery surface.
6. A-TRAC (Active Traction Control)
  During rugged off-road driving, this function controls the engine output and the brake fluid pressure that is applied to slipping wheels, and distributes the drive force that would have been lost through the slippage to the remaining wheels in order to achieve an LSD (Limited Slip Differential) effect. As a result, the vehicle's off-road drivability and ability to free itself from bumps have been increased.
  
  HINT:
  
  The A-TRAC system operates when 4WD mode is selected (4WD vehicles only).
7. AUTO-LSD (Auto Limited Slip Differential) (2WD Vehicles Only)
  The AUTO LSD operates with the VSC OFF switch on and the accelerator pedal depressed.
  
  The TRAC system restrains brake pressure and reduces differential movement, thus transmitting the drive torque to the other drive wheel to ensure stability under the following conditions:
  - Wheels run off the road.
  - Drive wheels run idle when starting on a slope with one wheel on snow/ice.
  HINT:
  
  Depressing the brake pedal cancels control of the AUTO LSD system.
8. CRAWL (Crawl Control)
  Crawl control is a system that provides assistance when driving on bumpy off-road surfaces, slippery road surfaces, etc. When crawl control is operating, the engine output and braking force are controlled automatically to enable driving while maintaining a constant speed. As a result, the driver can concentrate on steering the vehicle without having to operate the accelerator and brake pedals very much.
ABS with EBD, BA, TRAC, AUTO LSD, A-TRAC and VSC OPERATION
1. The skid control ECU 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 hydraulic brake booster) should be implemented.
INITIAL CHECK
1. When the vehicle speed first reaches approximately 6 km/h (4 mph) or more after the ignition switch is turned ON, each solenoid valve and the motor of the hydraulic brake booster 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.

FUNCTION OF COMPONENTS

Components	Functions
Speed Sensor	Detects the wheel speed of each wheel.
Hydraulic Brake Booster	Upon receiving a brake control signal from the skid control ECU, the hydraulic brake booster controls the hydraulic circuit and sends hydraulic pressure to each wheel. The master cylinder solenoid (skid control ECU) is removable.
Master Cylinder Solenoid (Skid Control ECU)	Detects the vehicle condition based on signals from the sensors and sends a brake control signal to the hydraulic brake booster.
Motor Relay	Supplies a power source to the pump motor.
Solenoid Relay	Supplies a power source to each solenoid.
Steering Angle Sensor	Detects the steering angle and amount of movement of the steering wheel, and then sends signals to the skid control ECU.
Yaw Rate and Deceleration Sensor	Detects the vehicle's yaw rate and deceleration and sends a signal to the skid control ECU.
Master Cylinder Pressure Sensor	Built into the master cylinder solenoid. Detects the pressure inside the master cylinder.
Accumulator Pressure Sensor	Built into the master cylinder solenoid and detects the accumulator pressure.
ECM	Sends sensor signals (throttle opening angle, engine speed) to the skid control ECU. The engine is controlled based on a traction control signal from the skid control ECU.
VSC OFF Switch	Enables the driver to select normal mode, TRAC OFF mode or VSC OFF mode.
A-TRAC Switch*1	Allows the driver to turn A-TRAC on and off.
Crawl Control Switch*2	The ON/OFF switch of the crawl control switch turns crawl control on and off and the speed selector switch of the crawl control switch changes the control mode.
ABS Warning Light	Illuminates to inform the driver that a malfunction in the ABS has occurred. w/ Rear Differential Lock: When the rear differential lock is in the lock state, ABS is also prohibited and the ABS warning light turns on.
BRAKE Warning Light	Illuminates to inform the driver that the parking brake is applied when the system is normal, and when the amount of brake fluid has decreased. Illuminates to inform the driver that a malfunction in the EBD has occurred.
TRAC OFF Indicator Light	Illuminates to inform the driver when the vehicle is in TRAC OFF mode.
VSC OFF Indicator Light	Illuminates to inform the driver that VSC OFF mode is entered using the VSC OFF switch.
Slip Indicator Light	Illuminates to inform the driver that a malfunction has occurred in the TRAC or VSC system. Blinks to inform the driver that TRAC, VSC, A-TRAC, AUTO LSD or CRAWL.
Crawl Indicator Light*2	Illuminates to inform driver that crawl control is ready to operate.
AUTO LSD Indicator Light*3	Illuminates to inform the driver that AUTO LSD is ready to operate.
A-TRAC Indicator Light*1	Illuminates to inform driver that A-TRAC is ready to operate.
VSC Buzzer	Housed in the combination meter assembly Sounds intermittently to inform driver if temperature of hydraulic brake booster has increased excessively due to continuous operation of TRAC, A-TRAC, AUTO LSD and CRAWL. Sounds continuously to alert driver that hydraulic pressure of accumulator in hydraulic brake booster has decreased.

*1: w/ A-TRAC
*2: w/ CRAWL
*3: for 2WD