Lexus RX300 (MCU15). Service manual — part 57

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CHASSIS — BRAKES

101

Item

Brake Assist

Not Activated

Brake Assist

Activated

(2)

Master Cylinder Cut Solenoid Valve
(Front)

OFF

OFF

(7)

Port: (A), (F)

Open

Open

(3)

Master Cylinder Cut Solenoid Valve
(Front, Rear)

OFF

ON

(6)

Port: (B), (E)

Open

Close

(4)

Reservoir Cut
Solenoid Valve

OFF

ON

(5)

Port: (C), (D)

Close

Open

(8), (9)

Pressure Holding Valve
(Front, Rear)

OFF

OFF

(10), (11)

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

Open

Open

(12), (13)

Pressure Reduction Valve
(Front, Rear)

OFF

OFF

(14), (15)

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

Close

Close

Skid Control ECU

1) Vehicle Stability Control

Based on the 4 types of sensor signals received from the speed sensors, yaw rate sensor, deceleration
sensor and steering sensor, the skid control ECU calculates the amount of vehicle condition.
If a strong understeer or oversteer tendency is created during an emergency avoidance maneuver or corner-
ing, and the skid control ECU determines that the amount of vehicle condition exceeds a prescribed
value, it controls the engine torque control through fuel cutoff and the brake fluid pressure according
to the amount of the vehicle condition.

Start to Fuel Cutoff Control

Start to Brake Control

Brake Control Completed

Fuel Cutoff
Control Completed

→ Time

Brake Wheel
Cylinder Fluid
Pressure*

Engine Torque

Level of Strong
Under Steering
or Over Steering

Amount of
Vehicle
Condition

↑

↔

↑

151CH31

Open

Close

High

*: The wheel cylinder that activates varies depending on the condition of the vehicle.

CHASSIS — BRAKES

102

2) Initial Check

After the ignition is turned ON, and the vehicle attains an approximate speed of 6 km/h (4 mph) or
more only at first time, the skid control ECU performs an initial check.
The functions of each solenoid valve and pump motor in the actuator are checked in order.

3) Self-Diagnosis

If the skid control ECU detects a malfunction in the VSC system, the warning light that corresponds
to the function in which the malfunction has been detected lights up, as indicated in the table below,
to alert the driver of the malfunction. The ECU will also store the codes of the malfunctions. The
DTCs (Diagnostic Trouble Codes) can be accessed through the blinking of the VSC warning light or
the use of a hand-held tester. For details, see the LEXUS RX300 Chassis & Body Repair Manual (Pub.
No. RM785E).

Item

ABS

TRC

VSC

EBD

Brake

Assist

ABS Warning Light

f

—

—

—

f

Brake System Warning Light

—

—

—

f

—

VSC Warning Light

f

f

f

—

—

4) Fail Safe

In the event of a malfunction in the skid control ECU turns on the ABS warning light and the VSC
warning light and prohibits the ABS, TRC, VSC and Brake Assist control. In the case of the malfunction
that the EBD control can not be carried out, the ECU also turns on the brake system warning light and
prohibits the EBD control.

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CHASSIS — STEERING

103

STEERING

JDESCRIPTION

The engine revolution sensing type rack and pinion power steering is used. In addition, the same tilt mecha-
nism and energy absorbing mechanism are used.

187CH22

RHD Model

" Specifications A

Item

RHD

LHD

Gear Ratio (Overall)

15.7

16.0

No. of Turns Lock to Lock

2.82

2.60

Rack Stroke

mm (in.)

137.2 (5.40)

126.4 (4.98)

Fluid Type

ATF Type DEXRON

R

II or III

z

CHASSIS — STEERING

104

JENERGY ABSORBING MECHANISM

The energy absorbing mechanism in the steering column consists of a lower bracket, breakaway bracket,
energy absorbing plate and a contractile main shaft. The steering column is mounted onto the instrument
panel reinforcement via a lower bracket and breakaway bracket which is supported via a capsule and energy
absorbing plate. The steering column and the steering gear box are connected with a contractile intermediate
shaft. Operational examples of this mechanism are follows.
When the steering gear box moves during a collision (primary collision), the main shaft and the intermediate
shaft contract, thus reduce the chance that the steering column and the steering wheel protrude into the
cabin.
When an impact is transmitted to the steering wheel in a collision (secondary collision), the steering wheel
and the driver airbag help absorb the impact. In addition, the breakaway bracket and the lower bracket
separate, causing the entire steering column to move foward.
At this time, the energy absorbing plate becomes deformed to help absorb the impact of the secondary
collision.

Energy
Absorbing Plate

Deform

Primary
Collision

Secondary
Collision

Breakaway Bracket

Lower Bracket

187CH23