Toyota Tacoma 2015-2018 Service Manual: System Description

Toyota Tacoma 2015-2018 Service Manual / Brake Control / Dynamic Control Systems / Vehicle Stability Control System(for Vacuum Brake Booster) / System Description

SYSTEM DESCRIPTION

1. 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.

(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.

(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) AUTO-LSD (Auto Limited Slip Differential)

When the vehicle is in H2 (2WD) 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 system operates when H2 (2WD) mode is selected.

(g) 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.

(h) 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.

2. 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, 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	Motor Relay	Supplies power to the pump motor.
Skid Control ECU	Solenoid Relay	Supplies power to the solenoid valves.
Speed Sensor		Detects the wheel speed of each of the 4 wheels.
VSC OFF Switch		Switches off the TRAC and VSC operation.
Stop Light Switch Assembly		Detects the brake pedal depressing signal.
ECM		Sends the throttle position signal, accelerator pedal position signal and engine speed signal to the skid control ECU. Controls the engine output based on the signals received from the skid control ECU.
Airbag Sensor Assembly	Yaw Rate and Acceleration Sensor	Detects the vehicle's yaw rate. Detects the vehicle's acceleration in the forward, rearward and lateral directions.
Spiral cable with sensor 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. When the rear differential lock is in the lock state, the ABS is also prohibited and the ABS warning light turns on.*2
	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 TRAC off mode is selected. When the rear differential lock is in the lock state, the TRAC is also prohibited and the TRAC OFF message is displayed.*2
	VSC OFF Indicator Light	Illuminates to inform the driver when VSC off mode is selected. When the rear differential lock is in the lock state, the VSC is also prohibited and the VSC OFF indicator light turns on.2 When the 4WD control switch (transfer position switch) set to L4, the VSC is also prohibited and the VSC OFF indicator light turns on.1
	Slip Indicator Light	Blinks to inform the driver when the TRAC, VSC system and/or trailer sway control is performing control. Illuminates to alert the driver when the skid control ECU detects a malfunction in the TRAC and/or VSC system, hill-start assist control, trailer sway control. Illuminates to inform the driver when the rear differential cannot be unlocked for 2 consecutive trips.*2
	AUTO LSD indicator light	Illuminates to inform the driver that AUTO LSD is ready to operate.
	VSC Warning Buzzer	Housed in the combination meter assembly Sounds intermittently to inform the driver if the temperature of brake actuator assembly has increased excessively due to continuous operation of AUTO LSD.
Brake Master Cylinder Reservoir Assembly	Brake Fluid Level Warning Switch	Detects the brake fluid level.
Millimeter Wave Radar Sensor Assembly		Sends brake request signals to the skid control ECU.

*1: for 4WD
*2: w/ Rear Differential Lock

Precaution

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System Diagram

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