Lexus ES300 (1997 year). Manual — part 16

62

CHASSIS — BRAKES

ABS & TRAC ECU

1) Wheel Speed Control

The ABS & TRAC ECU constantly receives signals from the 4 speed sensors and calculates the speed
of each wheel and vehicle speed.
During sudden acceleration or driving on a slippery surface, if the drive wheels (front wheels) start to slip,
the difference in speed between the drive wheels and the non-drive wheels (rear wheels) becomes greater,
causing the ECU to determine that the drive wheels are slipping.
Then, the ABS & TRAC ECU executes the right and left independent control of the front wheel brakes,
the engine torque control through fuel cutoff, and shift timing control, according to the extent of the slip.
TRAC operation processes are described below.

The vehicle speed is determined by way of the rear wheel speed. This speed is then compared to the
speed of the front wheels, which are the drive wheels, to determine the slip condition of the drive
wheels (front wheels).

The target control speed for the drive wheels is set based on the estimated vehicle speed.

If the speed of the front wheels, which are the drive wheels, exceeds the control starting speed, the ABS
& TRAC ECU determines that a slip has occurred and cuts off fuel according to the number of
cylinders. By executing engine torque control and brake control in this manner, the system regulates
the speed so that the front wheels attain the target control speed. In addition, the system executes
control to prohibit the shifting of the automatic transaxle at this time.

TRAC control ends when the drive wheels move to a non-slippery surface or when the driver releases
the accelerator pedal.

63

CHASSIS — BRAKES

2) Initial Check

An initial check is carried out once every a few seconds after the ignition was turned on. The function of
each solenoid valve and pump motor in the actuator are checked in order.

3) Self-Diagnosis

If the ABS & TRAC ECU detects a malfunction in the engine, ABS or TRAC system, it blinks the TRAC
OFF indicator light to alert the driver of the malfunction. At the same time, the ABS & TRAC ECU turns
the ABS warning light on. The ECU will also store the codes of the malfunctions. See the 1997 ES300
Repair Manual (Pub. No. RM511 U) for the diagnostic code check method, diagnostic code and diagnostic
code clearance.

4) Fail-Safe

In the event of a malfunction in the engine, ABS or TRAC system, the ABS & TRAC ECU prohibits the
TRAC system.
Thus, the brake and engine controls will operate in the same conditions as those without the TRAC
system.

64

CHASSIS — SUSPENSION

SUSPENSION

DESCRIPTION

As in the previous model, the new model uses MacPherson strut type independent suspension for both front
and rear.
An electric modulated suspension has been made newly available on all models as an option. The items given
below have been changed from the previous model.

The caster angle has been changed on the front suspension.

The mounting method of the front suspension stabilizer has been changed.

The mounting position of the rear suspension’s lower arm has been changed and its roll center height has
been changed.

The rear suspension upper support has been changed.

Specifications

Model

New

Previous

Item

New

Previous

Tread

mm (in)

1550 (61.0)

←

F

t

Caster

*

1

degrees

2

°

15

′

1

°

15

′

Front
Suspension

Camber

*

1

degrees

–0

°

40

′

←

Suspension

Toe–In

*

1

degrees

0

←

King Pin Inclination

*

1

degrees

13

°

05

′

←

R

Tread

mm (in)

1520 (59.8)

1500 (59.1)

Rear
Suspension

Camber

*

1

degrees

–0

°

45

′

–0

°

30

′

Suspension

Toe–In

*

1

mm (in)

4 (0.16)

←

*

1

:Unloaded Vehicle Condition

65

CHASSIS — SUSPENSION

FRONT SUSPENSION

1. General

As in the previous model, the new model uses MacPherson strut type independent suspension.
However, each part of suspension has been revised to realize excellent riding comfort, in addition, this
provides excellent stability and controllability.

2. Geometry

The caster angle has been increased to realize
excellent directional stability and steering
response.