Lexus SC300 / Lexus SC400. Manual — part 55

FRONT AIRBAG SENSOR

1.

Never reuse the front airbag sensors involved in a collision
when the airbag has deployed. (Replace both the left and
right airbag sensors.)

2.

Install the front airbag sensor with the arrow on the sensor
facing toward the front of the vehicle.

3.

The front airbag sensor set bolts have been anti–rust treated.
When the sensor is removed, always replace the set bolts
with new ones.

4.

The front airbag sensor is equipped with an electrical connection check mechanism. Be sure to lock this
mechanism securely when connecting the connector. If the connector is not securely locked, a malfunction
code will be detected by the diagnosis system (See page

AB–7

).

SPIRAL CABLE (in COMBINATION SWITCH)

The steering wheel must be fitted correctly to the steering column with the spiral cable at the neutral posi-
tion, otherwise cable disconnection and other troubles may result. Refer to page

AB–17

of this manual con-

cerning correct steering wheel installation.

STEERING WHEEL PAD (with AIRBAG)

1.

When removing the steering wheel pad or handling a new
steering wheel pad, it should be placed with the pad top
surface facing up.
In this case, the twin–lock type connector lock lever should be
in the locked state and care should be taken to place it so the
connector will not be damaged. And do not store a steering
wheel pad on top of another one. (Storing the pad with its me-
tallic surface up may lead to a serious accident if the airbag
inflates for some reason.)

2.

Never measure the resistance of the airbag squib.
(This may cause the airbag to deploy, which is very dangerous.)

AB–3

SRS

AIRBAG – General Description

3. Grease

should not be applied to the steering wheel pad and the pad should not be cleaned with detergents

of any kind.

4.

Store the steering wheel pad where the ambient temperature remains below 93

°

C (200

°

F), without high

humidity and away from electrical noise.

5.

When using electric welding, first disconnect the airbag connector (yellow color and 2 pins) under the
steering column near the combination switch connector before starting work.

6.

When disposing of a vehicle or the steering wheel pad alone, the airbag should be deployed using an SST
before disposal (See page

AB–91

). Perform the operation in a place away from electrical noise.

CENTER AIRBAG SENSOR ASSEMBLY

The connector of the center airbag sensor assembly should be connected or disconnected with the sensor
mounted on the floor. It the connector is connected or disconnected while the center airbag sensor assem-
bly is not mounted to the floor, it could cause undesired ignition of the airbag system.

WIRE HARNESS AND CONNECTOR

The airbag system wire harness is integrated with the cowl wire harness assembly. The wires for the airbag
wire harness are encased in a yellow corrugated tube. All the connectors for the system are also a standard
yellow color. If the airbag system wire harness becomes disconnected or the connector becomes broken
due to an accident, etc., repair or replace it as shown on page

AB–20

.

AB–4

SRS

AIRBAG – General Description

OPERATION

FUNCTION OF COMPONENTS

1.

FRONT AIRBAG SENSOR
A front airbag sensor is mounted inside each of the front
fenders. The sensor unit is a mechanical type. When the sen-
sor detects deceleration force above a predetermined limit in
a collision, the contacts in the sensor make contact, sending
a signal to the center airbag sensor assembly. The sensor
cannot be disassembled.

2.

SPIRAL CABLE (in COMBINATION SWITCH)
A spiral cable is used as an electrical joint from the vehicle
body side to the steering wheel.

3.

STEERING WHEEL PAD (with AIRBAG)
The inflater and bag of the airbag system are stored in the
steering wheel pad and cannot be disassembled.
The inflater contains a squib, igniter charge, gas generant,
etc., and inflates the bag in case of a frontal collision.

4. AIRBAG

WARNING

LIGHT

The airbag warning light is located on the combination meter.
It goes on to alert the driver of trouble in the system when a
malfunction is detected in the center airbag sensor assembly
self–diagnosis. In normal operating condition when the igni-
tion switch is turned to the ACC or ON position, the light goes
on for about 6 seconds and then goes off.

5.

CENTER AIRBAG SENSOR ASSEMBLY
The center airbag sensor assembly is mounted on the floor
inside the center cluster. The center airbag sensor assembly
consists of a center airbag sensor, safing sensors, ignition
control and drive circuit, diagnosis circuit, etc. It receives sig-
nals from the airbag sensors, judges whether the airbag must
be activated or not and diagnoses system malfunctions.

AB–5

– Operation

SRS

AIRBAG

6. AIRBAG

CONNECTORS

All connectors in the airbag system are colored yellow to distinguish them from other connectors. Connec-
tors having special functions and specifically designed for airbags are used in the locations shown below
to ensure high reliability. These connectors use durable gold–plated terminals.

Terminal Twin–Lock Mechanism

Airbag Activation Prevention Mechanism

Electrical Connection Check Mechanism

Connector Twin–Lock Mechanism

(1)

Terminal Twin–Lock Mechanism
Each connector has a two–piece construction consisting
of a housing and a spacer. This design secures the lock-
ing of the terminal by two locking devices (the spacer
and the lance) to prevent terminals from coming out.

(2)

Airbag Activation Prevention Mechanism
Each connector contains a short spring plate. When the connector is disconnected, the short spring
plate automatically connects the power source and grounding terminals of the squib.

AB–6

SRS

AIRBAG – Operation