Lexus SC300 / Lexus SC400. Manual - part 56

HINT: The illustration shows connectors (3) and (4). Connector (1) has a short spring plate on the fe-
male terminal side, but the operating principle is the same.

(3)

Electrical Connection Check Mechanism
This mechanism is designed to electrically check if con-
nectors are connected correctly and completely.
The electrical connection check mechanism is designed
so that the connection detection pin connects with the
diagnosis terminals when the connector housing lock is
in the locked condition.

HINT: The illustration shows connector (5). Connector (1) also has the same operating principle.

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 AIRBAG   –   Operation

(4) Connector Twin–Lock Mechanism

With this mechanism connectors (male and female connectors) are locked by two locking devices to
increase connection reliability. If the primary lock is incomplete, ribs interfere and prevent the second-
ary lock.

When the vehicle is involved in a frontal collision in the hatched area (Fig. 1) and the shock is larger than a prede-
termined level, the airbag is activated automatically. Safing sensors are designed to go on at a smaller decelera-
tion rate than the front and center airbag sensors. As illustrated in Fig. 2 below, ignition is caused when current
flows to the squib, which happens when a safing sensor and a front airbag sensor and/or the center airbag sen-
sor go on simultaneously.
When a deceleration force acts on the sensors, it causes the squib to ignite. Gas is then generated, increasing
the pressure inside the bag rapidly. The inflated bag breaks open the steering wheel pad. Bag inflation then
ends, and the gas is discharged through discharge holes provided behind the bag. The bag becomes deflated
as a result.

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 AIRBAG   –   Operation

INSPECTION ITEMS AND REPLACEMENT REQUIREMENTS

If a Vehicle is brought in for an airbag system inspection, or if a vehicle which has been involved in a collision
is inspected, perform the inspection in accordance with the following procedure. If any problems are discovered,
replace the affected part with a new one.

Steering Wheel Pad (with Airbag), Steering Wheel and Spiral
Cable

INSPECTION ITEMS

1. 

VEHICLES NOT INVOLVED IN A COLLISION
(a)  Perform a diagnostic system check (See page 

AB–30

).

(b)  Perform a visual check which includes the following items with

the steering wheel pad (with airbag) installed in the vehicle.

•

Check for cuts, minute cracks or marked discoloration of
the steering wheel pad top surface and grooved portion.

2. 

VEHICLES INVOLVED IN A COLLISION
IF THE AIRBAG IS NOT DEPLOYED
(a)  Perform a diagnostic system check (See page 

AB–30

).

(b)  Perform a visual check which includes the following items with

the steering wheel pad (with airbag) removed from the vehicle.

•

Check for cuts or cracks in, or marked discoloration of the
steering wheel pad top surface and grooved portion.

•

Check for cuts and cracks in, or chipping of connectors and
wire harnesses.

•

Check for deformation of the horn button contact plate of
the steering wheel.

HINT:

•

If the horn button contact plate of the steering wheel is
deformed, never repair it. Always replace the steering
wheel assembly with a new one.

•

There should be no interference between the steering
wheel pad and the steering wheel, and the clearance
should be uniform all the way around when the new
steering wheel pad is installed on the steering wheel.

CAUTION: For removal and installation of the steering wheel
pad, see page 

AB–14

, “REMOVAL AND INSTALLATION” and be

sure to follow the correct procedure.
IF THE AIRBAG IS DEPLOYED
(a)  Perform a diagnostic system check (See page 

AB–30

).

(b)  Perform a visual check which includes the following items with

the steering wheel pad (with airbag) removed from the vehicle.

•

Check for deformation of the horn button contact plate of
the steering wheel.

•

Check for damage to the spiral cable connector and wire
harness.

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 AIRBAG   –   Inspection Items and Replacement Requirements

HINT:

•

If the horn button contact plate of the steering wheel is deformed, never repair it. Always replace the
steering wheel assembly with a new one.

•

There should be no interference between the steering wheel pad and the steering wheel, and the
clearance should be uniform all the way around when the new steering wheel pad is installed on the
steering wheel.

REPLACEMENT REQUIREMENTS

In the following cases, replace the steering wheel pad, steering wheel or spiral cable.
CAUTION: For replacement of the steering wheel pad, see page 

AB–16

, “REMOVAL AND INSTALLA-

TION” and be sure to follow the correct procedure.

•

If the airbag has been deployed.

•

If the steering wheel pad or spiral cable has been found to be faulty in troubleshooting.

•

If the steering wheel pad, steering wheel or spiral cable has been found to be faulty during the check
in item 1–(b) or 2–(b).

•

If the steering wheel pad has been dropped.

Front Airbag Sensor

INSPECTION ITEMS

1. 

VEHICLES NOT INVOLVED IN A COLLISION

•

Perform a diagnostic system check (See page 

AB–30

).

2. 

VEHICLES INVOLVED IN A COLLISION
(a)  Perform a diagnostic system check (See page 

AB–30

).

(b)  If the front fender of the car or its periphery is damaged,

perform visual check for damage to the front airbag
sensor, which includes the following items even if the
airbag was not deployed:

•

Bracket deformation.

•

Peeling of paint from the bracket.

•

Cracks, dents or chips in the case.

•

Cracks and dents in, or chipping and scratches of
the connector.

•

Peeling off of the label or damage to the series
number.

Also refer to the body dimension drawings on page

BO–133

 and check the dimensions and mounting sur-

face angle of the body area where the front airbag sen-
sors are mounted.

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 AIRBAG   –   Inspection Items and Replacement Requirements