LEXUS SC400 1991 Service Repair Manual

wAlways tie down the steering wheel pad with the pad
side facing upward. It is very dangerous if the steer-
ing wheel pad is tied down with the metal surface
facing upward as the wire harness will be cut by the
shock of the airbag deploying and the steering
wheel pad will be thrown into the air.
HINT:
w The disc wheel will be marked by airbag deployment, so
use a redundant disc wheel.
4. CONFIRM FUNCTIONING OF SST (SEE PAGE AB±94)
SST 09082±0700
5. INSTALL SST CAUTION: Place the disc wheel on level ground.
(a) Connect the SST connector to the steering wheel pad
connector.
SST 09082±00700
NOTICE: To avoid damaging the SST connector and wire
harness, do not lock the secondary lock of the twin lock.
Also, provide some slack for the SST wire harness inside
the disc wheel.
(b) Move the SST to at least 10 m (33 ft) away from the steering wheel pad tied down on the disc wheel.
6. COVER STEERING WHEEL PAD WITH CARDBOARD BOX OR TIRES
(Covering Method Using Cardboard Box)
Cover the steering wheel pad with the cardboard box and
weigh the cardboard box down in four places with a at least
20 kg (44 lb, 196 N).
Size of cardboard box: Must exceed the following dimen-
sions ±x = 460 mm (18.11 in.)
When dimension y of the cardboard box exceeds
the diameter of the disc wheel with tire the steering
wheel pad is tied to±
x = 460 mm (18.11 in.) + width of tire
y = 650 mm (25.59 in.)
NOTICE: If a cardboard box smaller than the size speci-
fied is used, the cardboard box will be broken by the
shock of the airbag deployment.
±
SRS AIRBAG Disposal of Steering Wheel Pad (with Aribag)AB±95
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(Covering Method Using Tires)
Place at least three tires without disc wheel on top of the disc
wheel with tire to which the steering wheel pad is tied.
Tire size: Must exceed the following dimensions ±Width 185 mm (7.28 in.)
Inner diam 360 mm (14.17 in.)
CAUTION: Do not use tires with disc wheels.
NOTICE: The tires may be marked by the airbag deploy-
ment, so use redundent tires.
7. AIRBAG DEPLOYMENT (a) Connect the SST red clip to the battery positive (+)terminal and the black clip to the battery negative (±)
terminal.
(b) Confirm that no±one is within 10 m (33 ft) of the disc wheel the steering wheel pad is tied to.
(c) Press the SST activation switch and deploy the airbag.
HINT: The airbag deploys simultaneously as the LED of the
SST activation switch lights up.
8. DISPOSAL OF STEERING WHEEL PAD (WITH AIRBAG) CAUTION:
w The steering wheel pad is very hot when the airbag is
deployed, so leave it alone for at least 30 minutes after de-
ployment.
w Use gloves and safety glasses when handling a steering
wheel pad with deployed airbag.
w Do not apply water, etc. to a steering wheel pad with
deployed airbag.
w Always wash your hands with water after completing the
operation.
(a) Remove the steering wheel pad from the disc wheel.
(b) Place the steering wheel pad in a vinyl bag, tie the end
tightly and dispose of it the same way as other general
parts.
AB±96
±
SRS AIRBAG Disposal of Steering Wheel Pad (with Aribag)
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CONFIRM FUNCTIONING OF SST
When deploying the airbag, always use the specified SST:
SRS AIRBAG DEPLOYMENT TOOL.
SST 09082±00700
1. CONNECT SST TO BATTERY Connect the red clip of the SST to the battery positive (+) ter-
minal and the black clip to the battery negative (±) terminal.
HINT: Do not connect the yellow connector which connects
with the airbag system.
2. CONFIRM FUNCTIONING OF SST Press the SST activation switch, and confirm the LED of the
SST activation switch lights up.
CAUTION: If the LED lights up when the activation switch
is not being pressed, SST malfunction is probable, so
definitely do not use the SST.
±
SRS AIRBAG Disposal of Steering Wheel Pad (with Aribag)AB±97
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SERVICE SPECIFICATIONS
SERVICE DATA
TerminalFront airbag sensor resistance

S ±
A755±885

S
A

S ± S
755 885



S ± ALess than 1

TORQUE SPECIFICATIONS
Part tightenedNVmkgf Vcmft Vlbf
Steering wheel3536026Steering wheel
Steering wheel pad
35
7.4
360
75
26
65 in. Vlbfg
Front airbag sensor25260 19g
Center airbag sensor assembly131309
AB±98±
SRS AIRBAG Disposal of Steering Wheel Pad (with Airbag)
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SRS AIRBAG
AB±1INTRODUCTION
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GENERAL DESCRIPTION
The LEXUS SC400 is equipped with an SRS (Supplemental Restraint System) a\
irbag.
Failure to carry out service operations in the correct sequence could cause the\
airbag system to unex-
pectedly deploy during servicing, possibly leading to a serious accident.
Further, if a mistake is made in servicing the airbag system, it is possible the\
airbag may fail to operate
when required.
Before performing servicing (including removal or installation of parts, insp\
ection or replacement), be
sure to read the following items carefully, then follow the correct procedure described in the repair
manual.
1. Malfunction symptoms of the airbag system are difficult to confirm, so the diagnostic codes become themost important source of information when troubleshooting.
When troubleshooting the airbag system, always inspect the diagnostic co\
des before disconnecting the
battery (See page AB±25).
2. Work must be started after approx. 20 seconds or longer from the time the ig\
nition switch is turned to the LOCK position and the negative (±) terminal cable is disconnec\
ted from the battery. (The
airbag system is equipped with a back±up power source so that if work is sta\
rted within 20 seconds
of disconnecting the negative (±) terminal cable of the battery, the airbag may be deployed.)
When the negative (±) terminal cable is disconnected from the battery, memory of the clock and audio sys-
tems will be cancelled. So before starting work, make a record of the conten\
ts memorized by the audio
memory system. Then when work is finished, reset the audio systems as before a\
nd adjust the clock. When
the vehicle has power tilt and power telescopic steering, power seat, power \
outside rear view mirror and
power shoulder belt anchorage, which are all equipped with memory function, it\
is not possible to make
a record of the memory contents. So when the work is finished, it will be\
necessary to explain this fact to
the customer, and ask the customer to adjust the features and reset the memory. To avoid erasing the
memory of each memory system, never use a back±up power supply from outside\
the vehicle.
3. Even in cases of a minor collision where the airbag does not deploy, the front airbag sensors and
the steering wheel pad should be inspected (See page AB±9).
4. Never use airbag parts from another vehicle. When replacing parts, replace them with new parts.
5. Before repairs, remove the airbag sensors if shocks are likely to be applied to the sensors during repairs.
6. Never disassemble and repair the front airbag sensors, center airbag sensor a\
ssembly or steering
wheel pad in order to reuse it.
7. If the front airbag sensors, center airbag assembly or steering wheel pa\
d have been dropped, or if there are cracks, dents or other defects in the case, bracket or conn\
ector, replace them with new
ones.
8. Do not expose the front airbag sensors, center airbag sensor assembly or\
steering wheel pad directly to hot air or flames.
9. Use a volt/ohmmeter with high impedance (10 kW/V minimum) for troubleshoo\
ting of the electrical circuit.
10. Information labels are attached to the periphery of the airbag components. Follow t\
he instructions
on the notices.
11. After work on the airbag system is completed, perform the airbag warning\
light check (See page AB±30 ).
AB±2
SRS AIRBAG
± General Description
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FRONT AIRBAG SENSOR
1. Never reuse the front airbag sensors involved in a collisionwhen 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 sur\
e 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 pa\
ge 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±3SRS AIRBAG ± General Description
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3. Grease should not be applied to the steering wheel pad and the pad should not b\
e 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 shou\
ld 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 d\
isconnected 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 ass\
embly. 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 connecto\
r becomes broken
due to an accident, etc., repair or replace it as shown on page AB±20.
AB±4
SRS AIRBAG
± General Description
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OPERATION
FUNCTION OF COMPONENTS
1. FRONT AIRBAG SENSORA 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 f rom the airbag sensors, judges whether the airbag must
be activated or not and diagnoses system malfunctions. AB±5
± OperationSRS AIRBAG
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6. AIRBAG CONNECTORSAll 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 MechanismEach 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±6SRS AIRBAG ± Operation
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