Toyota Tundra Service Manual: System Description

SYSTEM DESCRIPTION

FUNCTION DESCRIPTION

(a) 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.

(b) 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.

(c) 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.

(2) If the brake booster malfunctions and the skid control ECU (brake actuator assembly) judges that the brake pedal force applied by the driver is not sufficient to ensure adequate braking force, brake assist is used to enhance the braking force.

(d) 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.

(e) 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.

(f) Hill-start Assist Control

(1) When starting uphill, this control maintains the brake hydraulic pressure to the 4 wheels, in order to momentarily help to prevent the vehicle from descending backward.

(g) Trailer Sway Control

(1) If the vehicle is towing a trailer with an inappropriate hitch load, trailer sway could be caused by crosswinds, imbalance caused by the load, or the driver's steering. Trailer sway control reduces trailer sway by controlling the engine output and the braking of each wheel.

(h) AUTO LSD (Auto Limited Slip Differential)

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

The AUTO LSD system is used to restrain brake pressure and reduce differential movement, thus transmitting drive torque to the other drive wheel to ensure startability under the following conditions:

  • Wheels run off the road.
  • Drive wheels slip when starting on a slope with one wheel on snow/ice.

HINT:

Depressing the brake pedal cancels control of the AUTO LSD system.

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, 2 reservoir 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

ABS Motor Relay

Supplies power to the pump motor.

ABS Solenoid Relay

Supplies power to the solenoid valves.

Speed Sensor

Detects the wheel speed of each of the 4 wheels.

Stop Light Switch Assembly

Detects the brake pedal depressing signal.

VSC OFF Switch (Traction Control Switch)

  • For 2WD vehicles or 4WD vehicles in 2H mode: Operation of the VSC OFF switch (traction control switch) changes the vehicle from normal mode to TRAC OFF mode to AUTO LSD mode to VSC OFF mode.
  • For 4WD vehicles in 4H or 4L mode: Operation of the VSC OFF switch (traction control switch) changes the vehicle from normal mode to VSC OFF mode.

ECM

  • Sends the throttle position signal, accelerator pedal position signal, engine speed signal etc. to the skid control ECU.
  • Based on the signals from the skid control ECU, controls the engine output.

Airbag Sensor Assembly

Yaw Rate and Acceleration Sensor

  • The airbag sensor assembly incorporates the yaw rate sensor and acceleration sensor.
  • The yaw rate sensor detects the vehicle's yaw rate.
  • The acceleration sensor detects the vehicle's longitudinal and lateral acceleration.
  • The airbag sensor assembly sends the detection signals from the yaw rate sensor and acceleration sensor to the skid control ECU via CAN communication.

Spiral with Sensor Cable Sub-assembly

Steering Angle 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 Warning Light

  • 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.

TRAC OFF Indicator Light

  • Illuminates to inform the driver when VSC OFF mode is entered.
  • for 4WD:

    Illuminates to inform the driver when TRAC OFF mode is entered.

VSC OFF Indicator Light

Illuminates to inform the driver when VSC OFF mode or AUTO LSD mode is entered.

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.

AUTO LSD indicator light

Illuminates to inform the driver that AUTO LSD is ready to operate

Brake Master Cylinder Reservoir Sub-assembly

Brake Fluid Level Warning Switch

Detects the brake fluid level.

Brake Pedal Support Assembly

Brake Pedal Load Sensing Switch

Detects the brake pedal load.

    Slip Indicator Light Remains ON

    System Diagram

    See More:

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