Lexus ES300 (1997 year). Manual — part 14

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CHASSIS — BRAKES

4. Layout of Components

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CHASSIS — BRAKES

5. Function of Components

No.

Component

Function

Slip Indicator Light

Blinks to inform the driver when the TRAC system
is operated.

TRAC OFF Indicator Light

Lights to inform the driver when the TRAC system
is turned OFF by the TRAC OFF switch. And,
blinks to alert the driver when the ECU detects the
malfunction in the TRAC system.

ECM

Sends signals to the ABS & TRAC ECU, such as

the throttle valve opening angle, specific volume
of intake air signal, etc.

Controls the engine output and shift timing in

accordance with the fuel cutoff request and shift
timing request that are output by the ABS &
TRAC ECU.

ABS & TRAC ECU

Judges the vehicle driving condition based on
signals from 4 speed sensors and signals from
ECM, and sends fuel cut and shift timing demand
signals to the ECM and brake control signal to the
ABS & TRAC actuator.

ABS & TRAC Actuator

Controls the brake fluid pressure to each brake
wheel cylinder of the driving wheel (front wheel) by
signals from the ABS & TRAC ECU.

ABS & TRAC
Relay

Solenoid Relay

Directs electricity to the solenoid valves in the
actuator.

Relay

Pump Motor Relay

Controls the pump motor operation in the actuator.

Speed Sensors (Front and Rear)

Detect the wheel speed of each of four wheels.

Throttle Position Sensor

Detects the throttle valve opening angle.

TRAC OFF Switch

Turns the TRAC system inoperative.

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CHASSIS — BRAKES

6. Construction and Operation of Components

TRAC OFF Switch and Indicator Light

1) TRAC OFF Switch

When pressed, this switch turns the TRAC system inoperative. Pressing it again changes it to operative.
It is always operative right after the engine is restarted.

2) TRAC OFF Indicator Light

This light goes on when the TRAC system is set inoperative by the TRAC OFF switch, and informs the
driver accordingly. And, blinks to alert the driver when a malfunction has occurred in the engine and
TRAC system.

3) Slip Indicator Light

When the TRAC system is operative, this light blinks and informs the driver accordingly.

ABS & TRAC Actuator

1) Construction

The ABS & TRAC actuator consists of 12 two-position solenoid valves, I motor 2 pumps, 2 reservoir and
2 pressure regulator valves.
The 12 two-position solenoid valves consist of 2 master cut solenoid valves, 2 reservoir cut solenoid
valves, 4 pressure holding valves, and 4 pressure reduction valves.
Pressure regulator valve is assembled into the master cut solenoid valve.
The basic construction and operation of the pump, reservoir pressure holding valve, and pressure
reduction valve are shared with the ABS.

a. Master Cut Solenoid Valve

When the TRAC system is active, a signal from the ABS & TRAC ECU causes the master cut solenoid
valve to turn ON in order to shut off the circuit between the master cylinder and the front brake wheel
cylinder.
The basic construction and operation are the same as those of the pressure holding valve.

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CHASSIS — BRAKES

b. Reservoir Cut Solenoid Valve

When the TRAC system is active, a signal from the ABS & TRAC ECU causes the reservoir cut
solenoid valve to turn ON in order to open the circuit from the master cylinder to the pump.
The basic construction and operation are the same as those of the pressure reduction valve.

c.

Pressure Regulator Valve

Regulates the brake fluid pressure generated by the pump to a pressure level needed for TRAC control.

2) Hydraulic Circuit

*: Pressure regulator valve is assembled into the master cut solenoid valve, however, it is illustrated

separately to explain its operation.