LEXUS SC400 1991 Service Repair Manual

RSOOU±02
WIRING DIAGRAM
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SUPPLEMENTAL RESTRAINT SYSTEM DESCRIPTIONRS±7
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CENTER AIRBAG SENSOR ASSEMBLY CONNECTOR
RS00V±0B
 No. Symbol Terminal Name A ± Electrical Connection Check Mechanism B ± Electrical Connection Check Mechanism 1 P± Squib (Passenger) 2 P+ Squib
(Passenger) 3 D+ Squib
(Driver) 4 D± Squib  (Driver) 5 E1 Ground 6 E2 Ground 7 Tc Diagnosis 8 +SR Front Airbag Sensor RH
 9 ±SR Front Airbag Sensor RH  10 ±SL Front Airbag Sensor LH  11 +SL Front Airbag Sensor LH
 12 LA SRS Warning Light 13 IG2 Power Source (IGN Fuse) 14 ACC Power Source (CIG Fuse)
RS±8±
SUPPLEMENTAL RESTRAINT SYSTEM DESCRIPTION
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OPERATION
FUNCTION OF COMPONENTS
RS02M±04
1. STEERING WHEEL PAD (with AIRBAG)The inflater and bag of the supplemental restraint system are
stored in the steering wheel pad and cannot be disas-
sembled. The inflater contains a squib, igniter charge, gas
generant, etc., and inflates the bag in case of frontal collision.
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. FRONT PASSENGER AIRBAG ASSEMBLY The inflater and bag of the supplemental restraint system are
stored in the front passenger airbag assembly 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. SRS WARNING LIGHT The SRS 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.
In normal operating conditions when the ignition switch is
turned to the ACC or ON position, the light goes on for about
6 seconds and then goes off.
5. FRONT AIRBAG SENSOR A front airbag sensor is mounted inside each of the front fend-
ers. The sensor unit is a mechanical type. When the sensor
detects deceleration force above a predetermined limit, con-
tacts is m ade in the sensor, sending a signal to the center air-
bag sensor assembly. The sensor cannot be disassembled.
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SUPPLEMENTAL RESTRAINT SYSTEM OPERATIONRS±9
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6. CENTER AIRBAG SENSOR ASSEMBLYThe 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 sensor, diagnosis
circuit and ignition control, drive circuit, etc.
It receives signals from the airbag sensors, judges whether
the SRS must be activated or not.
7. SRS CONNECTORS
 No. Item Application
 (1) Terminal Twin±Lock Mechanism Connectors
,  ,  ,  ,  ,  , 
 (2) Airbag Activation Prevention Mechanism Connectors
,  ,  , 
 (3) Electrical Connection Check Mechanism Connectors
,  ,  (4) Connector Twin±Lock Mechanism Connectors  ,  , 
All connectors in the supplemental restraint system are col-
ored yellow to distinguish them from other connectors. Con-
nectors having special functions and specifically designed
for SRS are used in the locations shown below to ensure high
reliability. These connectors use durable gold±plated termi-
nals.
RS±10
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SUPPLEMENTAL RESTRAINT SYSTEM OPERATION
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(1) Terminal Twin±Lock MechanismEach connector has a two±piece construction consisting of
a housing and a spacer. This design secures the locking 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 con-
nector is disconnected, the short spring plate automatically
connects the power source and grounding terminals of the
squib.
HINT: The illustration shows connectors ,  and  . Con-
nector

has short spring plates on the female terminal side.
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SUPPLEMENTAL RESTRAINT SYSTEM OPERATIONRS±11
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(3) Electrical Connection Check MechanismThis mechanism is designed to electrically check if connec-
tors are connected correctly and completely. The electrical
connection check mechanism is designed so that the con-
nection detection pin connects with the diagnosis terminals
when the connector housing lock is in the locked condition.
HINT: The illustration shows connectors  and  Connector,
also has the same operating principle.
RS±12
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SUPPLEMENTAL RESTRAINT SYSTEM OPERATION
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(4) Connector Twin±Lock MechanismWith this mechanism connectors (male and female connec-
tors) are locked by 2 locking devices to increase connection
reliability. If the primary lock is incomplete, ribs interfere and
prevent the secondary lock.
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SUPPLEMENTAL RESTRAINT SYSTEM OPERATIONRS±13
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When the vehicle is involved in a frontal collision in the
hatched area (Fig. 1) and the shock is larger than a predeter-
mined level, the SRS is activated automatically. A safing sen-
sor is designed to go on at a smaller deceleration rate than
the front and center airbag sensors. As illustrated in Fig. 2,
ignition is caused when current flows to the squib, which hap-
pens when a safing sensor and a front airbag sensor and/or
the center airbag sensor go on simultaneously. When a de-
celeration force acts on the sensors, two squibs in the driver
airbag and front passenger airbag ignite and generate gas.
The gas discharging into the driver and front passenger air-
bags rapidly increases the pressure inside the bags breaking
open the steering wheel pad and instrument panel door.
Bag inflation then ends, and the bags deflate as the gas is
discharged through discharge holes at the bag's rear or side.
RS±14±
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PREPARATION
SST (SPECIAL SERVICE TOOLS)
RS00X±04
RECOMMENDED TOOLS
RSOOY±04
EQUIPMENT
RS00Z±04\
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Torque wrench 
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Bolt Length: 35 mm (1.38 in.) Pitch: 1.0 mm (0.039 in.)
Diam.: 6.0 mm (0.236 in.) 

Airbag disposal
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Tire Width: 185 mm (7.28 in.) Inner diam.: 360mm (14.17 in.) Airbag disposal
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Tire with disk wheel Width: 185 mm (7028 in.)
Inner diam.: 360 mm (14.17 in.) 


Airbag disposal
\
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Vinyl bag Airbag disposal
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SUPPLEMENTAL RESTRAINT SYSTEM PREPARATIONRS±15
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STEERING WHEEL PAD AND
SPIRAL CABLE
INSPECTION ITEMS
RS04B±01
1. VEHICLES NOT INVOLVED IN A COLLISION
(a) Perform diagnostic system check. (See page RS±59)
(b) Perform a visual check which includes the following items with the steering wheel pad (with airbag installed in the
vehicle.
wCheck 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 RS±59)
(b) Perform a visual check which includes the following items with the steering wheel pad (with airbag) removed from the
vehicle.
wCheck for cuts or cracks in, or marked discoloration of
the steering wheel pad top surface and grooved portion.
w Check for cuts and cracks in, or chipping of connectors
and wire harness.
w Check for deformation of the horn button contact plate
of the steering wheel.
HINT:
w 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.
w 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 RS±18, ªSTEERING WHEEL PAD
AND SPIRAL CABLE REMOVAL AND INSTALLATIONº
and be sure to follow the correct procedure.
RS±16
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SUPPLEMENTAL RESTRAINT SYSTEM STEERING WHEEL PAD AND SPIRAL CABLE
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