System Description

WARNING: This page is about a different car, the 2006 Toyota Tundra and 2005 Toyota Tundra. However, it is still accessible from the selected car via links, so may be relevant.

GENERAL
- A newly developed hydraulic brake booster unit, which has been made compact and lightweight through the integration of the skid control ECU and the actuator, has been newly adopted.
- An active speed sensor, which is capable of detecting extremely low speeds, has been adopted.
SYSTEM DESCRIPTION
HINT:

The yaw rate and deceleration sensors are combined and in a single unit. This unit communicates with the skid control ECU through CAN communication.
1. ABS with EBD & BA & TRAC & VSC operation
  1. The skid control ECU calculates vehicle stability tendency based on signals from the speed sensor, yaw rate & deceleration sensor and 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 wheel brake pressure by the brake actuator) should be implemented.
  2. The SLIP indicator blinks and the VSC buzzer sounds to inform the driver that the VSC system is operating. The SLIP indicator also blinks when TRAC is operating, and the operation being performed is displayed.
DRIVE MODES
The control conditions of the drive modes and functions are as follows:

4WD:

Fig 1: Control Conditions Of Drive Modes And Functions (4WD)
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

2WD:

Fig 2: Control Conditions Of Drive Modes And Functions (2WD)
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
ACTIVE SAFETY
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.
  
  Fig 3: Operation Diagram - ABS (Anti-Lock Brake System)
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  
  Operation description
  
  The skid control ECU detects wheel lock condition by receiving vehicle speed signals from each speed sensor, and sends control signals to the pump motor and solenoid valve. The pump motor and solenoid valve avoid wheel lock by controlling the oil pressure of each wheel cylinder.
  
  The ABS warning light comes on when the ABS system is malfunctioning.
2. EBD (Electronic Brake force Distribution)
  The EBD control utilizes ABS, realizing proper brake force distribution between front and rear wheels in accordance with driving conditions.
  
  In addition, when braking while cornering, it also controls the brake forces of the right and left wheels, helping to maintain vehicle behavior.
  
  Fig 4: Operation Diagram - EBD (Electronic Brake Force Distribution)
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  
  Operation description
  
  The skid control ECU receives the speed signal from each speed sensor to detect the slip condition of the wheels and sends the control signal to the solenoid valves.
  
  The solenoid valve controls the oil pressure of the rear wheel cylinder and splits the control power properly between the rear wheels and the right and left wheels.
  
  Both of the ABS and BRAKE warning lights come on to indicate a malfunction in the EBD system.
3. BA (Brake Assist)
  The primary purpose of the brake assist system is to provide an auxiliary brake force to assist the driver who cannot generate a large enough brake force during emergency braking, thus helping to maximize the vehicle's braking performance.
  
  Fig 5: Operation Diagram - BA (Brake Assist)
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  
  Operation description
  
  The skid control ECU receives the speed signal from each speed sensor and the oil pressure signal from the master cylinder pressure sensor to determine whether brake assist is necessary or not. If brake assist is deemed necessary, the skid control ECU sends control signals to the pump motor and solenoid. The pump and the solenoid valve then control pressure applied to each wheel cylinder.
  
  The ABS warning light comes on to indicate a malfunction in the BA system.
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.
  
  Fig 6: Operation Diagram - VSC (Vehicle Stability Control)
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  
  Operation description
  
  The skid control ECU determines vehicle condition by receiving signals from the speed sensor, yaw rate & deceleration sensor and steering angle sensor. The skid control ECU controls engine torque through the ECM via CAN communication, and oil pressure through the pump and solenoid valve.
  
  The SLIP indicator light blinks and the skid control (VSC warning) buzzer sounds when the system is operating. Both the VSC TRAC warning light and the VSC OFF indicator light (4WD) come on to indicate a malfunction in the VSC system.
DRIVING PERFORMANCE
1. 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 off or accelerating on a slippery surface.
  
  Fig 7: Operation Diagram - TRAC (Traction Control)
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  
  Operation description
  
  The skid control ECU detects the vehicle's slip condition by receiving signals from the speed sensor and ECM via CAN communication. The skid control ECU controls engine torque through the ECM via CAN communication, and oil pressure through the pump and solenoid valve.
  
  The SLIP indicator light blinks when the system is operating. Both the VSC TRAC warning light and SLIP indicator light come on to indicate a malfunction in the TRAC system.
2. A-TRAC (Active Traction Control) (4WD)
  During rugged off road driving, this function controls the engine output and the brake fluid pressure that is applied to the slipping wheel, 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 driveability and ability to free itself from the mogul have been increased.
  
  HINT:
  
  The A-TRAC system will operate when 4WD mode is selected (4WD vehicles only).
  
  Fig 8: Operation Diagram - A-TRAC (Active Traction Control) (4WD)
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  
  Operation description
  
  The SLIP indicator light blinks when the system is operating. Both the VSC TRAC warning light and SLIP indicator light come on to indicate a malfunction in the A- TRAC system.
3. AUTO LSD (Auto Limited Slip Differential)
  If the vehicle enters 2WD mode, the AUTO LSD will operate with the AUTO LSD switch on and the accelerator pedal depressed.
  
  The TRAC system is used to restrain brake pressure and reduce differential move, thus transmitting drive torque to the other drive wheel to ensure startability 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.

The AUTO LSD system will operate when 2WD mode is selected (4WD vehicles only).

Fig 9: Operation Diagram - Auto LSD (Auto Limited Slip Differential)
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Operation description

The SLIP indicator light blinks and AUTO LSD indicator light comes on when the system is operating. Both the VSC TRAC warning light and SLIP indicator light come on to indicate a malfunction in the AUTO LSD system.