Lexus ES300 (2002 year). Manual — part 110

CHASSIS – BRAKE

CH-66

208CH28

Master Cylinder

Master Cylinder
Pressure Sensor

Master Cylinder
Pressure Sensor

Pumps

Front Left

Rear Right

Reservoirs

Rear Left

Front Right

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

(12)

(13)

(14)

8. Brake Actuator

Construction

The brake actuator consists of 14 two-position valves, 1 motor, 2 pumps, and 2 reservoirs, and 2 master
cylinder pressure sensor.
The 14 two-position solenoid valves consists of 2 master cylinder cut solenoid valve [(1), (6)], 2 suction
solenoid valves [(2), (5)], 2 reservoir cut solenoid valves [(3), (4)], 4 pressure holding valves [(7), (8), (9),
(10)], and 4 pressure reduction valves [(11), (12), (13), (14)].

Hydraulic Circuit

CHASSIS – BRAKE

CH-67

208CH30

Speed Sensor

Master Cylinder
Pressure Sensor

Stop Light
Switch

Skid Control

ECU

Brake
Actuator

ABS Warning
Light

ABS with EBD Operation

The ABS with EBD operation is the same as the operation of the ABS with EBD system. Refer to that system
for details.

Brake Assist Operation

The fluid pressure that has been generated by the pump in the brake actuator is directed to the wheel
cylinders. By applying a greater fluid pressure than the master cylinder, a greater braking force is achieved.

System Diagram

CHASSIS – BRAKE

CH-68

208CH29

Master Cylinder

Master Cylinder
Pressure Sensor

Master Cylinder
Pressure Sensor

Port (B)

Port (A)

Port (C)

Port (D)

Port (E)

Port (F)

Port (H)

Port (G)

Port (I)

Port (J)

Port (L)

Port (K)

Port (M)

Port (N)

Pumps

Front Left

Rear Right

Reservoirs

Rear Left

Front Right

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

(12)

(13)

(14)

Item

Brake Assist

Not Activated

Brake Assist

Activated

(1) (6)

Master Cylinder Cut Solenoid Valve

OFF (Open)

ON*

(1), (6)

Port: (A), (F)

OFF (Open)

ON*

(3) (4)

Reservoir Cut Solenoid Valve

OFF (Close)

OFF (Close)

(3), (4)

Port: (C), (D)

OFF (Close)

OFF (Close)

(2) (5)

Suction Solenoid Valve

OFF (Close)

ON (Open)

(2), (5)

Port: (B), (E)

OFF (Close)

ON (Open)

(7), (8),

Pressure Holding Valve

OFF (Open)

OFF (Open)

(7), (8),

(9), (10)

Port: (G), (H), (I), (J)

OFF (Open)

OFF (Open)

(11), (12),

Pressure Reduction Valve

OFF (Close)

OFF (Close)

(11), (12),

(13), (14)

Port: (K), (L), (M), (N)

OFF (Close)

OFF (Close)

*: The solenoid valve controls the hydraulic pressure between “open” through “close” according to the

operating condition by adjusting continually.

CHASSIS – BRAKE

CH-69

187CH41

208CH31

Speed Sensor

Skid Control

ECU

ECM

Brake Actuator

Slip Indicator Light

Master Cylinder

Master Cylinder
Pressure Sensor

Master Cylinder
Pressure Sensor

Port (A)

Port (B)

Port (C)

Port (D)

Port (E)

Port (F)

Port (G)

Port (H)

Port (I)

Port (J)

Port (K)

Port (L)

Port (M)

Port (N)

Pumps

Front Left

Rear Right

Reservoirs

Rear Left

Front Right

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

(12)

(13)

(14)

TRAC Operation

The fluid pressure that is generated by the pump is regulated by the master cylinder cut solenoid valve to
the required pressure. Thus, the wheel cylinder of the drive wheels are controlled in the following 3 modes:
pressure reduction, pressure holding, and pressure increase modes, to restrain the slippage of the drive
wheels.
The diagram below shows the hydraulic circuit in the pressure increase mode when the TRAC system is
activated.
In other, the pressure holding valve and the pressure reduction valve are turned ON / OFF according to the
ABS operation pattern described on the previous page.

System Diagram