sensor LEXUS SC300 1991 Service Repair Manual

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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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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FRONT AIRBAG SENSOR
INSPECTION ITEMS
RS015±0C
1. VEHICLES NOT INVOLVED IN A COLLISIONPerform a diagnostic system check.
(See page RS±59)
2. VEHICLES INVOLVED IN A COLLISION
(a) Perform a diagnostic system check. (See page RS±59)
(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:
wBracket deformation.
w Peeling of paint from the bracket.
w Cracks, dents or chips in the case.
w Cracks and dents in, or chipping and scratches of the
connector.
w Peeling off of the label or damage to the series number.
Also refer to the body dimension drawings in the BODY sec-
tion and check the dimensions and mounting surface angle
of the body area where the front airbag sensors are mounted.
(The SRS may malfunction, or may not work, if the mounting
angle or dimensions of the sensor mount are not correct.)
REPLACEMENT REQUIREMENTS
RS016±06
In the following cases, replace the front airbag sensor.
NOTICE: for replacement of the front airbag sensor, see
page RS±42 , ªFRONT AIRBAG SENSOR REMOVAL AND
INSTALLATIONº and be sure to follow the correct proce-
dure.
w If the SRS has been deployed in a collision.
(Replace both the left and right airbag sensors.)
w If the front airbag sensor has been found to be faulty in
troubleshooting.
w If the front airbag sensor has been found to be faulty
during the check in item 2±(b).
w If the front airbag sensor has been dropped.
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SUPPLEMENTAL RESTRAINT SYSTEM FRONT AIRBAG SENSORRS±41
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COMPONENTS
RS045±01
FRONT AIRBAG SENSOR
REMOVAL AND INSTALLATION
RS046±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.
w Never reuse the sensor involved in a collision when the
SRS has deployed.
w Never repair a sensor in order to reuse it.
RS±42±
SUPPLEMENTAL RESTRAINT SYSTEM FRONT AIRBAG SENSOR
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1. DISCONNECT NEGATIVE (±) TERMINAL CABLE FROMBATTERY
CAUTION: Work must be started after 90 seconds from
the time the ignition switch is turned to the ªLOCKº posi-
tion and the negative (±) terminal cable is disconnected
from the battery.
(See page RS±2)
2. REMOVE ENGINE UNDER COVER
(See page BO±12)
3. REMOVE FRONT AIRBAG SENSOR
(a) Disconnect the connector.
(b) Remove the bolt, the nut and the sensor.
4. INSTALL FRONT AIRBAG SENSOR
(a) Install the sensor with the arrow on the sensor facing toward the front of the vehicle.
Torque: 25 N Vm (260 kgf Vcm, 19 ft Vlbf)
NOTICE:
w Make sure the sensor is installed to the specified torque.
w If the sensor has been dropped, or there are cracks, dents
or other defects in the case, brackets or c onnector,
replace the sensor is removed, always replace the set bolt
and the nut with new one.
w The sensor set bolt and the nut have been anti±rust
treated. When the sensor is removed, always replace the
set bolt and the nut with new ones.
w After installation, shake the sensor to check that there is
no looseness.
w The front sensor is equipped with an electrical
connection check mechanism. Be sure 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.
w Check that the dimensions of the body where the front
airbag sensor is installed match those in the body
dimension drawings in the BODY section.
(The SRS may malfunction, or may not work, if the
dimensions of the sensor mount is not correct.)
5. INSTALL ENGINE UNDER COVER
6. CONNECT NEGATIVE (±) TERMINAL CABLE TO BATTERY
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SUPPLEMENTAL RESTRAINT SYSTEM FRONT AIRBAG SENSORRS±43
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CENTER AIRBAG SENSOR
ASSEMBLY
INSPECTION ITEMS
RS047±01
1. VEHICLES NOT INVOLVED IN A COLLISIONPerform a diagnostic system check.
(See page RS±59)
2. VEHICLES INVOLVED IN A COLLISION
IF THE SRS IS NOT DEPLOYED
Perform a diagnostic system check.
(See page RS±59)
IF THE SRS IS DEPLOYED
Replace the center airbag sensor assembly.
REPLACEMENT REQUIREMENTS
RS019±06
In the following cases, replace the center airbag sensor as-
sembly.
NOTICE: For replacement of the center airbag sensor as-
sembly, see page RS±46 ªCENTER AIRBAG SENSOR
ASSEMBLY REMOVAL AND INSTALLATIONº and be sure
to follow the correct procedure.
w If the SRS has been deployed in a collision.
w If the center airbag sensor assembly has been found to
be faulty in troubleshooting.
w If the center airbag sensor assembly has been dropped.
RS±44
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SUPPLEMENTAL RESTRAINT SYSTEM CENTER AIRBAG SENSOR ASSEMBLY
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COMPONENTS
RS048±01
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SUPPLEMENTAL RESTRAINT SYSTEM CENTER AIRBAG SENSOR ASSEMBLYRS±45
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CENTER AIRBAG SENSOR ASSEMBLY
REMOVAL AND INSTALLATION
RS049±01
NOTICE:
wDo not open the cover or the case of the ECU and various
computers unless absolutely necessary. (If the IC
terminals are touched, the IC may be destroyed by static
electricity.)
w Never use SRS parts from another vehicle. When
replacing parts, replace with new parts.
w Never reuse the center airbag sensor assembly involved
in a collision when the airbag has deployed.
w Never repair a sensor in order to reuse it.
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).
2. REMOVE AND INSTALL CENTER AIRBAG SENSOR ASSEMBLY
(a) Using a torx wrench, loosen and tighten the 3 screws.
Torx wrench: T40 (Part No. 09042±00020 or locally manufac-
tured tool)
(b) Disconnect and connect the connector. NOTICE: Removal and installation of the connector is
done with the sensor assembly installed.
(c) Using a torx wrench, tighten the 3 screws. Torx wrench: T40 (Part No. 09042±00020 or locally manufac-
tured tool)
Torque: 15 N Vm (150 kgf Vcm, 11 ft Vlbf)
NOTICE:
w Make sure the sensor assembly is installed to the
specified torque.
w If the sensor assembly has been dropped, or there are
cracks, dents or other defects in the case, bracket or
connector, replace the sensor assembly with a new one.
w When installing the sensor assembly, take care that the
airbag wiring does not interfere with other parts and is
not pinched between other parts.
w After installation, shake the sensor assembly to check
that there is no looseness.
RS±46±
SUPPLEMENTAL RESTRAINT SYSTEM CENTER AIRBAG SENSOR ASSEMBLY
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REPLACEMENT REQUIREMENTS
RS01D±07
In the following cases, replace the wire harness or connector.
wIf any part of the SRS wire harness or any connector has
been found to be faulty in troubleshooting.
w If any part of the SRS wire harness or any connector has
been found to be faulty during the check in items 2±(b)
or (c).
NOTICE:
w If the wire harness used in the SRS is damaged, replace
the whole wire harness assembly.
w When the connector to the WIRE HARNESS AND CON-
NECTORs can be repaired alone (when there is no
damage to the wire harness), use the repair wire specially
designed for the purpose.
SENSOR REPLACEMENT
REPAIR WIRE FOR FRONT AIRBAG
RS04A±01
Repair wire with 2 pressure±contact sleeves
(Part No. 82988±24010) has been prepared for exclusive
use in repairing connector damage etc. caused by frontal col-
lision of the vehicle.
When repairing the WIRE HARNESS AND CONNECTOR
connector on the wire harness side, always use the special
repair wire.
NOTICE: Do not replace the connector housing or termi-
nal only.
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 ªLOCKº posi-
tion and the negative (±) terminal cable is disconnected
from the battery.
(See page RS±2)
2. DISCONNECT WIRE HARNESS AT VEHICLE SIDE
(a) Remove the cover at the rear of the connector housing and expose the wire harness.
(b) Cut the wire harness behind the connector housing. HINT: The operation is performed more easily if the wire har-
ness is left as long as possible.
RS±48
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SUPPLEMENTAL RESTRAINT SYSTEM WIRE HARNESS AND CONNECTOR
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