steering LEXUS SC400 1991 Service Repair Manual

GENERAL DESCRIPTION
The LEXUS SC400/300 is equipped with an SRS (Supplemental Restraint System\
) such as the driver
airbag and front passenger airbag. Failure to carry out service operations in \
the correct sequence
could cause the SRS to unexpectedly deployed during servicing, possibly leadin\
g to a serious acci-
dent. Further, if a mistake is made in servicing the supplemental restraint system, i\
t is possible the
SRS may fail to operate when required. Before performing servicing (inc\
luding removal or installa-
tion of parts, inspection or replacement), be sure to read the followin\
g items carefully, then follow
the correct procedure described in the repair manual.
1. Malfunction symptoms of the supplemental restraint system are difficult to confirm, so the diagnostic trouble codes become the most important source of information when troubleshooting. When
troubleshooting the supplemental restraint system, always inspect the diagnostic trouble codes before
disconnecting the battery (See page RS±59).
2. Work must be started after 90 seconds from the time the ignition switch turn\
ed to the LOCK position
and the negative (±) terminal cable is disconnected from the battery. (The supplemental restraint
system is equipped with a back±up power source so that if work is sta\
rted within 90 seconds of
disconnecting the negative (±) terminal cable of the battery, the SRS may be deployed.)
When the negative (±) terminal cable is disconnected from the battery, memory of the clock and audio sys-
tems will be canceled. So before starting work, make a record of the contents memo\
rized by the audio
memory system. When work is finished, reset the audio systems as before and ad\
just 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 custom-
er, 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 SRS does not deploy, the steering wheel pad, front passenger
airbag assembly, front airbag sensors and center airbag sensor assembly should be inspe\
cted (See pages
RS±16 , 28 , 41 and 44).
4. Never use SRS parts from another vehicle. When replacing parts, replace \
them with new parts.
5. Before repairs, remove the airbag sensor if shocks are likely to be applied to the sensors during r\
epairs.
6. Never disassemble and repair the steering wheel pad, front passenger airbag a\
ssembly, front airbag sensors or center airbag sensor assembly in order to reuse it.
7. If the steering wheel pad, front passenger airbag assembly, front airbag sensors or center airbag sensor assembly have been dropped, or if there are cracks, dents or dents or ot\
her defects in the case, bracket
or connector, replace them with new ones.
8. Do not expose the steering wheel pad, front passenger airbag assembly, front airbag sensors and center airbag sensor assembly directly to hot air or flames.
9. Use a volt/ohmmeter with high impedance (10 k
/V minimum) of troubleshooting of the system's electrical
circuit.
10. Information labels are attached to the periphery of the SRS components. \
Follow the instructions on the
notices.
11. After work on the supplemental restraint system is completed, perform the SRS\
warning light check (See page RS±59 ).
12. If the vehicle is equipped with a mobile communication system, refer to \
the precaution in the IN section. RS±2
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SUPPLEMENTAL RESTRAINT SYSTEM GENERAL DESCRIPTION
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STEERING WHEEL PAD (with AIRBAG)
RS00Q±07
1. When removing the steering wheel pad or handling a new steering wheel pad, it should be placedwith 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 steer\
ing wheel pad on top of another
one. (Storing the pad with its metallic surface up may lead to a serious ac\
cident if the airbag inflates for
some reason.
2. Never measure the resistance of the airbag squib. (This may cause the airbag\
to deploy, which isvery dangerous.)
3. Grease should not be applied to the steering wheel pad and the pad should not \
be cleaned withdetergents of any kind.
4. Store the steering wheel pad where the ambient temperature below 93
C (200
F), without high
humidity and away from electrical noise.
5. When using electric welding, first disconnect the SRS connector (yellow\
color and 2 pins) under the steering column near the combination switch connector before startin\
g 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 RS±21).
Perform the operation in a place away from electrical noise.
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SUPPLEMENTAL RESTRAINT SYSTEM GENERAL DESCRIPTIONRS±3
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SPIRAL CABLE (in COMBINATION SWITCH)
RS00P±06
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 RS±19 of this manual concerning correct steering wheel installation.
FRONT PASSENGER AIRBAG ASSEMBLY
RS00N±07
1. Always store a removed or new front passenger airbag assembly with the a\
irbag door facing up.
Store the airbag assembly with the airbag door facing down could cause a seri\
ous accident if the
airbag inflates.
2. Never measure the resistance of the airbag squib. (This may cause the airbag\
to deploy, which isvery dangerous.)
3. Grease should not be applied to the front passenger airbag assembly and \
the door should not be
cleaned with detergents of any kind.
4. Store the front passenger airbag assembly where the ambient temperature remai\
ns below 93
C
(200
F), without high humidity and away from electrical noise.
5. When using electric welding, first disconnect the SRS connector (yellow col\
or and 2 pins) installed
on the glove compartment door finish plate at upper side of the glove co\
mpartment assembly
before starting work.
6. When disposing of a vehicle or the front passenger airbag assembly alone\
, the airbag should be deployed using an SST before disposal (See page RS±34). Perform the operation in a place away
from electrical noise.
RS±4
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SUPPLEMENTAL RESTRAINT SYSTEM GENERAL DESCRIPTION
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DESCRIPTION
RS00S±02
The SRS (Supplemental Restraint System), together with the seat belt, is designed to help protect the driv-
er. Frontal inspect, the airbag sensor detect the shock, and if the front±\
to±rear shock is greater than a spe-
cified value, an airbag stored in the steering wheel pad is inflated ins\
tantaneously to help reduce the shock
to the driver.
LOCATION OF COMPONENTS
RS00T±02
RS±6±
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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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±
SUPPLEMENTAL RESTRAINT SYSTEM OPERATION
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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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IF THE AIRBAG IS 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 he
vehicle.
wCheck for deformation of the horn button contact plate
of the steering wheel.
w Check for damage to the spiral cable connector and wire
harness.
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 pad is installed on the steering wheel.
REPLACEMENT REQUIREMENTS
RS011±02
In the following cases, replace the steering wheel pad, steer-
ing wheel or spiral cable.
CAUTION: For replacement 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.
w If the airbag has been deployed.
w If the steering wheel pad or spiral cable has been found
to be faulty in troubleshooting.
w 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).
w If the steering wheel pad has been dropped.
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SUPPLEMENTAL RESTRAINT SYSTEM STEERING WHEEL PAD AND SPIRAL CABLERS±17
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COMPONENTS
RS04D±01
STEERING WHEEL PAD AND SPIRAL
CABLE REMOVAL AND INSTALLATION
RS04D±01
NOTICE:
wIf the wiring connector of the supplemental restraint
system is disconnected with the ignition switch at ON or
ACC, diagnostic trouble codes will be recorded.
w Never use SRS parts from another vehicle. When
replacing parts, replace with new parts.
1. DISCONNECT NEGATIVE (±) TERMINAL CABLE FROM
BATTERY
CAUTION: Work must be started after 90 seconds from
the time the ignition switch is turned to the LOCK posi-
tion and the negative (±) terminal cable is disconnected
from the battery (See page RS±2).
RS±18
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SUPPLEMENTAL RESTRAINT SYSTEM STEERING WHEEL PAD AND SPIRAL CABLE
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2. REMOVE STEERING WHEEL PAD
(a) Place the front wheels facing straight ahead.
(b) Using a torx wrench, loosen the 4 screws. Torx wrench: T30(Part No. 09042±00010 or locally manufactured tool)
(d) Loosen the torx screws until the groove along the screw circumference catches on the screw case.
(e) P u l l t h e w heel pad out from the steering wheel and
disconnect the SRS connector.
NOTICE: When removing the wheel pad, take care not to
pull the airbag wire harness.
CAUTION:
w When storing the wheel pad, keep the upper surface of
the pad facing upward (See pages RS±3).
w Never disassemble the wheel pad.
3. REMOVE STEERING WHEEL
(a) Disconnect the connector.
(b) Remove the set nut.
(c) Place matchmarks on the steering wheel and main shaft.
(d) Using SST, remove the steering wheel.
SST 09213±31021
4. REMOVE AND INSTALL SPIRAL CABLE FROM/TO COMBINATION SWITCH
(See page BE±51)
NOTICE: Do not disassemble the spiral cable or apply oil
to it.
5. CENTER SPIRAL CABLE
(a) Check that the front wheels are facing straight ahead.
(b) Turn the spiral cable c ounterclockwise by hand until it
becomes harder to turn the cable.
(c) Then rotate the spiral cable clockwise about 3 turns to align the red mark.
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SUPPLEMENTAL RESTRAINT SYSTEM STEERING WHEEL PAD AND SPIRAL CABLERS±19
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