service LEXUS SC400 1991 Service Owner's Manual

5Check harness between center airbag sensor assembly and front airbag
sensor.
(1) Disconnect center airbag sensor assembly
connector.
(2) Using service wires, connect +SR and ±SR, +SL and ±SL on the wire harness side of the
center airbag sensor assembly connector.
Measure resistance between terminals +SR and
±SL, +SL and ±SL of harness side connector of
front airbag sensor.

Lightly touch ohmmeter probes at
position shown in illustration.

Make sure the front airbag sensor con-
nector is properly connected.
Repair or replace harness or connector between
center airbag sensor assembly and front airbag
sensor (See page AB±20).
Replace front airbag sensor connector (See page AB±20)
NG
OK
Resistance: Below 1

AB±72±
SRS AIRBAG Troubleshooting
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NGOK
Check center airbag sensor assembly.3
(1) Disconnect negative (±) terminal cable from
battery, and wait at least 20 seconds.
(2) Turn ignition switch lock.
(3) Disconnect center airbag sensor assembly
connector.
(4) Using a service wire, connector terminal Tc of center airbag sensor assembly connector to
body ground.
(5) Install the center airbag sensor assembly.
(6) Connect negative (±) terminal cable to battery.
(7) Turn ignition switch ACC or ON.
Check operation of airbag warning light.
Airbag light comes on.
Check harness between center airbag sensor
assembly and TDCL or check connector.
Replace center airbag sensor assembly.
C
P
OK
CautionNever turn ignition switch ACC or ON and
never connect negative (±) terminal to battery
before the center airbag sensor assembly is
installed.
±
SRS AIRBAG TroubleshootingAB±89
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DISPOSAL OF STEERING WHEEL
PAD (WITH AIRBAG)
When scrapping vehicles equipped with an airbag system or dis-
posing of a steering wheel pad (with airbag), always first deploy
the airbag in accordance with the procedure described below.
If any abnormality occurs with the airbag deployment, contact the
SERVICE DEPT. of TOYOTA MOTOR SALES, U.S.A., INC..
Never dispose of a steering wheel pad which has an
undeployed airbag.
When disposing of a steering wheel pad with an airbag deployed
in a collision, follow the same procedure given under ªAIRBAG
DEPLOYMENT PROCEDURE (WHEN SCRAPPING THE VE-
HICLE), part 5, DISPOSAL OF STEERING WHEEL PAD (WITH
AIRBAG)º (See page AB±93).
PRECAUTIONS FOR AIRBAG DEPLOYMENT
1. The airbag produces a sizeable exploding sound when
it deploys, so perform the operation out±of±doors and
where it will not create a nuisance to nearby residents.
2. When deploying the airbag, always use the specified
SST; SRS AIRBAG DEPLOYMENT TOOL (SST
09082±00700). Perform the operation in a place away
from electrical noise.
3. When deploying an airbag, perform the operation from at least 10 m (33 ft) away from the steering wheel pad.
4. The steering wheel pad is very hot when the airbag is deployed, so leave it alone for at least 30 minutes after
deployment.
5. Use gloves and safety glasses when handling a steering
wheel pad with deployed airbag.
6. Always wash your hands with water after completing the operation.
7. Do not apply water, etc. to a steering wheel pad with deployed airbag.
AIRBAG DEPLOYMENT PROCEDURE
(WHEN SCRAPPING VEHICLE)
HINT: Have a battery ready as the power source to deploy the
airbag.
1. DISCONNECT NEGATIVE (±) TERMINAL CABLE FROM BATTERY
CAUTION: Work must be started after approx. 30 sec-
onds or lo nger from the time the ignition switch is turned
to the LOCK position and the negative (±) terminal cable
is disconnected from the battery (See page AB±2).
±
SRS AIRBAG Disposal of Steering Wheel Pad (with Airbag)AB±91
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3.14 X (Diameter)2
4
3. FIX STEERING WHEEL PAD TO DISC WHEEL WITH TIRE(a) Install bolts with washers in the four bolt holes in thesteering wheel pad.
Bolt: L 35.0 mm (1.4 in.) M 6.0 mm
Pitch 1.0 mm
NOTICE: Tighten the bolts by hand until the bolts
become difficult to turn.
Do not tighten the bolts too much.
(b) Using a service±purpose wire harness for vehicle, tie down the steering wheel pad to the disc wheel.
Wire harness: Stripped wire harness section 1.25 mm or
more (0.002 in. or more)
HINT: To calculate the square of the stripped wire harness
section ±
Square =
CAUTION: If a wire harness which is too thin or some oth-
er thing is used to tie down the steering wheel pad, it may
be snapped by the shock when the airbag is deployed,
this is highly dangerous. Always use a wire harness for
vehicle use which is at least 1.25 mm (0.002 in.).
(c) Using 3 wire harnesses, wrap the wire harnesses at least 2 times each around the bolts installed on the left
and right sides of the steering wheel pad.
CAUTION: Tightly wind the wire harness around the bolts
so that there is no slack.
If there is slackness in the wire harness, the steering
wheel pad may come loose due to the shock when the
airbag is deployed, this is highly dangerous.
(d) Face the upper surface of the steering wheel pad upward. Separately tie the left and right sides of the steering
wheel pad to the disc wheel through the hub nut holes.
Position the steering wheel pad connector so that it
hangs downward through a hub hole in the disc wheel.
CAUTION:
wMake sure that the wire harness is tight. It is very
dangerous if looseness in the wire harness results
in the steering wheel pad coming free through the
shock of the airbag deploying.
AB±94
±
SRS AIRBAG Disposal of Steering Wheel Pad (with Aribag)
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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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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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PREPARATION
SST (SPECIAL SERVICE TOOLS)
09082±00700SRS Airbag
Deployment Tool
09213±31021Crankshaft Pulley
Puller
09843±18020Diagnosis Check
Wiring
Steering wheel
RECOMMENDED TOOLS
09042±00010Torx Socket
T30
09042±00020Torx Socket
T30
09082±00015TOYOTA
Electrical Tester
Center airbag sensor assembly
Steering wheel pad
EQUIPMENT
Part NameNote
Torque wrench
AB±13SRS AIRBAG ± Preparation
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CLEARING OF DIAGNOSTIC CODE
1. CLEARING OF MALFUNCTION CODE(EXCEPT CODE 41)
Remove the battery negative (±) terminal or ECU±B fuse for
10 seconds or more with the ignition switch OFF.
NOTICE: When connecting the battery after cancelling
the malfunction code, always do it with the ignition
switch in LOCK position. If the battery is connected with
the ignition switch in ACC or ON position, there are cases
when the diagnosis system does not operate normally.
HINT:
wCode 41 cannot be cleared by this method.
wThe lower the temperature, the longer the battery
negative (±) terminal must be left off.
wOther memory systems (clock, audio system) will also
be cancelled out (See page AB±2).
2. CLEARING OF MALFUNCTION CODE 41 STORED IN MEMORY
(a) Connect service wires to terminals Tc and AB of theTDCL.
(b) Turn the ignition switch ACC or ON and wait approx. 6 seconds.
(c) S ta rtin g with th e Tc te rmin a l, ap p ly bo d y gr ound
alternately to terminal Tc and terminal AB twice each in
cycles of 1.0 ± 0.5 seconds. Finally, keep applying body
ground to terminal Tc.
HINT: When alternating between body ground of terminals Tc
and AB release one from body ground while applying it to the
other terminal. The time interval in between must be within
the following conditions. If it is out of the conditions, code 41
will not be cleared.
(d) After several seconds, when the airbag warning light
starts to blink in a 64 msec. cycle, cancellation is
completed.
HINT: This method clears not only code No. 41, but also other
malfunction codes all at once.
Except when instructed by the troubleshooting procedure,
use this method only when the repair procedure is completed
(See page AB±25).
AB±32
SRS AIRBAG
± Troubleshooting
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(1) Connect connector to center airbag sensorassembly.
(2) Using a service wire, connect D
+, D± on spiral
cable side of connector between spiral cable
and steering wheel pad.
(3) Connect negative (±) terminal cable to battery, and wait at least 2 seconds.
Check squib circuit.
Codes other than code 11 may be output at this
time, but this is not relevant.
Measure resistance between D+, D± on spiral cable
side of connector between spiral cable and steer-
ing wheel pad and body ground.
Go to step [ 8 ].
Diagnostic code 11 is not output.
Resistance: 1 M
or higher
Replace center airbag sensor assembly.
Check center airbag sensor assembly.
(1) Turn ignition switch ACC or ON and wait at
least 20 seconds.
(2) Using SST, connect terminals Tc and E
1 of
TDCL.
SST 09843±18020
(3) Check diagnostic code. AB±45
SRS AIRBAG
± Troubleshooting
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(1) Turn ignition switch LOCK.
(2) Disconnect negative (±) terminal cable frombattery.
(3) Connect connector to center airbag sensor assembly.
(4) Using a service wire, Connect D
+ and D± on
spiral cable side of connector between spiral
cable and steering wheel pad.
(5) Connect negative (±) terminal cable to battery, and wait at least 2 seconds.
Check squib circuit.
Codes other than code 12 may be output at this
time, but this is not relevant.
Measure voltage at D+ on spiral cable side of con-
nector between spiral cable and steering wheel
pad.
Go to step [ 7 ].
Resistance: 1 V
Replace center airbag sensor assembly.
Check center airbag sensor assembly.
(1) Turn ignition switch ACC or ON and wait at least 20 seconds.
(2) Using SST, connect terminals Tc and E
1 of
TDCL.
SST 09843±18020
(3) Check diagnostic code.
Diagnostic code 12 is not output. AB±51
SRS AIRBAG
± Troubleshooting
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