Toyota Tacoma manuals

Toyota Tacoma 2015-2018 Service Manual: System Description

SYSTEM DESCRIPTION

1. SYSTEM DESCRIPTION

HINT:

The skid control ECU is built into the hydraulic brake booster.

(a) 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.

(b) Multi-terrain Anti-lock Brake System (Multi-terrain ABS)

This function detects off-road driving in sand, mud, gravel, dirt and so on based on signals from the yaw rate and acceleration sensor, the speed sensor and the ECM, and then automatically switches to the ABS control most appropriate for the current road conditions.

(c) 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.

In addition, when braking while cornering, it also controls the brake forces of the right and left wheels, helping to maintain the vehicle stability.

(d) 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.

(e) 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.

HINT:

The TRAC system operates when H2 (2WD) mode is selected.

(f) A-TRAC (Active Traction Control)

During rugged off-road driving, this function controls 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 ruts have been increased.

HINT:

The A-TRAC system operates when L4 (Low speed 4WD) mode is selected.

(g) 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.

(h) Hill-start Assist Control

When the vehicle starts off on a steep hill, hill-start assist control detects the backward descent of the vehicle and effects 4-wheel hydraulic pressure control to reduce the speed of the vehicle.

For a Maximum of 5 seconds after the control starts, fluid pressure is gradually released and the control is complete.

HINT:

Depressing the brake pedal cancels control of the hill-start assist control system.

Does not operate when the shift lever in P or N, or when the vehicle is running/rolling back up a slope with the shift lever in R.

(i) 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.

(j) Multi-terrain Select Control

When multi-terrain select control is active, A-TRAC brake control and engine output control most appropriate for the selected road mode are performed automatically. In this way, superior off-road driveability is achieved.

(k) Trailer Sway Control

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

Components

Function

Speed sensor

Detects wheel speed of each wheel.

Hydraulic brake booster

Upon receiving brake control signal from skid control ECU (master cylinder solenoid), controls hydraulic circuit and sends hydraulic pressure to each wheel. Skid control ECU (master cylinder solenoid) removable.

Skid control ECU

(Master cylinder solenoid)

Detects vehicle condition based on signals from sensors and sends brake control signal to hydraulic brake booster.

Motor relay

Supplies power source to pump motor.

Solenoid relay

Supplies power source to each solenoid.

ABS warning light

Illuminates to inform driver that skid control ECU (master cylinder solenoid) has detected ABS system malfunction and terminated ABS system operation.

BRAKE warning light

Illuminates to inform driver that skid control (master cylinder solenoid) ECU has detected EBD system malfunction.

VSC OFF indicator light

Illuminates when vehicle is in VSC OFF mode.

TRAC OFF indicator light

Illuminates when vehicle is in TRAC OFF mode.

A-TRAC indicator light

Illuminates to inform driver that A-TRAC is ready to operate.

Slip indicator light

  • Blinks to inform driver that TRAC, VSC and AUTO LSD in operation.
  • Illuminates to inform driver that skid control ECU (master cylinder solenoid) has detected VSC system malfunction.

Crawl indicator light (for Automatic transmission)

Illuminates to inform the driver that crawl control is ready to operate.

Multi-terrain select indicator light (for Automatic transmission)

Illuminates to inform the driver that multi-terrain select control is ready to operate.

Multi-terrain select indicator (for Automatic transmission)

Displays the selected road surface mode.

Multi-information display (for Automatic transmission)

Displays multi-terrain select operation assist messages.

Informs the driver of the status of the crawl control operation.

VSC OFF switch

Operation of VSC OFF switch changes vehicle from normal mode to TRAC OFF mode to VSC OFF mode.

  • During normal mode, pressing VSC OFF switch for short amount of time changes vehicle to TRAC OFF mode.
  • When vehicle is stopped, pressing VSC OFF switch for 3 seconds or more changes vehicle to VSC OFF.

Crawl control switch (for Automatic transmission)

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.

Multi-function switch (for Automatic transmission)

Changes the display on the multi-information display.

Turns multi-terrain select control on and off.

Selects the road surface mode for multi-terrain select.

A-TRAC switch

Allows driver to turn A-TRAC on and off.

Yaw rate and acceleration sensor (Airbag sensor assembly)

Detects vehicle's yaw rate and acceleration and sends signal to skid control ECU (master cylinder solenoid).

Master cylinder pressure sensor

Built into hydraulic brake booster. Detects pressure inside master cylinder.

Accumulator pressure sensor

Built into master cylinder solenoid and detects accumulator pressure.

Steering angle sensor (Spiral cable with sensor sub-assembly)

Detects steering wheel's steering angle and amount of movement, then sends signal to skid control ECU (master cylinder solenoid).

ECM

  • Sends sensor signals (throttle opening angle, engine rpm) to skid control ECU (master cylinder solenoid).
  • Engine controlled based on traction control signal from skid control ECU (master cylinder solenoid).

VSC Warning Buzzer

  • Housed in the combination meter assembly
  • Sounds intermittently to inform the driver if the temperature of hydraulic brake booster has increased excessively due to continuous operation of TRAC, A-TRAC and AUTO LSD.
  • Sounds continuously to alert the driver that the hydraulic pressure of accumulator in the hydraulic brake booster has decreased.

Millimeter Wave Radar Sensor Assembly

Sends brake request signals to the skid control ECU.

How To Proceed With Troubleshooting
CAUTION / NOTICE / HINT Techstream can be used in steps 3, 6, 9 and 12. PROCEDURE 1. VEHICLE BROUGHT TO WORKSHOP NEXT ...

System Diagram
SYSTEM DIAGRAM Transmitting ECU (Transmitter) Receiving ECU Signals Communication Method ECM Skid control ECU ...

Other materials:

Fail-safe Chart
FAIL-SAFE CHART FAIL-SAFE FUNCTION (a) When a malfunction occurs in the lane departure alert system, a message will be displayed on the multi-information display in the combination meter assembly and the lane departure alert system will be disabled depending on the malfunction. War ...

Brake Booster Pump Motor on Time Abnormally Long (C1252)
DESCRIPTION The motor relay (semiconductor relay) is built into the master cylinder solenoid and drives the pump motor based on a signal from the skid control ECU (master cylinder solenoid). DTC No. DTC Detecting Condition Trouble Areas C1252 ...

ABS Warning Light does not Come ON
DESCRIPTION Refer to ABS Warning Light Remains ON (See page ). WIRING DIAGRAM Refer to ABS Warning Light Remains ON (See page ). CAUTION / NOTICE / HINT NOTICE: When replacing the skid control ECU (master cylinder solenoid), perform calibration (See page ). Inspect the ...

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