1991 LEXUS SC400 airbag

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
±
SUPPLEMENTAL RESTRAINT SYSTEM CENTER AIRBAG SENSOR ASSEMBLY
WhereEverybodyKnowsYourName

COMPONENTS
RS048±01
±
SUPPLEMENTAL RESTRAINT SYSTEM CENTER AIRBAG SENSOR ASSEMBLYRS±45
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName

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
±
SUPPLEMENTAL RESTRAINT SYSTEM WIRE HARNESS AND CONNECTOR
WhereEverybodyKnowsYourName

HOW TO PROCEED WITH TROUBLESHOOTING
Malfunction symptoms of the supplemental restraint system are difficult to confirm, so the diagnostic
trouble codes become the most important source of information when troubleshoot\
ing. Perform trouble-
shooting of the supplemental restraint system in accordance with the fol\
lowing procedure:
HINT: Do not disconnect the battery negative (±) terminal cable until st\
ep , Diagnostic Trouble Code
Check and Recording, has been completed.

CUSTOMER PROBLEM ANALYSIS
Using the CUSTOMER PROBLEM ANALYSIS CHECK SHEET (See page RS±58) for reference, ask the
customer in as much detail as possible about the problem.
WARNING LIGHT CHECK
Check the SRS warning light. If the light remains on, a malfunction is stored in the center airbag sensor,
assembly, so proceed to step . If the SRS warning light is not on, a malfunction has occurred in the SRS
warning light circuit, so perform troubleshooting for 22.
HINT: 22 is recorded when a malfunction occurs in the SRS warning light syst\
em.
If an open malfunction occurs in the SRS warning light system, the SRS w\
arning light does not light up,
so that until the malfunction is repaired, the diagnostic trouble codes (\
including 22) cannot be confirmed.
 DIAGNOSTIC TROUBLE CODE CHECK AND RECORDING
Check the di agnostic trouble codes and make a note of any malfunction codes which ar\
e output. If a normal
code is output, an abnormality in the power source circuit may have occurred\
, so perform troubleshooting
for source voltage in step .
If 22 is output, skip steps  and  and proceed to step .
 MALFUNCTION CODE CLEARANCE
Clear the malfunction code.
HINT: The malfunction code output in step  indicates that a malfunction has occurred in the circuit desig-
nated by the malfunction code, but does not indicate whether the malfunction \
is still occurring or whether
it was in the past.
Accordingly, it is necessary to find out the present condition of the malfunction oc\
currence by clearing the
malfunction code and performing the diagnostic code check again. If this\
operation is neglected and trou-
bleshooting is performed using only the malfunction code confirmed in step , isolating the problem com-
ponent becomes difficult and invites mistaken diagnosis.
 DIAGNOSTIC TROUBLE CODE CHECK AND RECORDING  SYMPTOM SIMULATION
After repeating ignition switch ON±OFF operation (ON: wait 20 secs, OFF: \
wait 20 secs.) 5 times, check
the diagnostic trouble codes. If any code is output, the malfunction is sti\
ll occurring, so proceed to step .
Bearing in mind that a malfunction code was registered in step , provided that the normal code is present-
ly output, use the methods described in step  to simulate the malfunction.
RS±54
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
WhereEverybodyKnowsYourName

NOTICE: When connecting the battery after clearing the malfunction code, always\
do it with the igni-
tion switch in LOCK position. When the battery has been reconnected, turn the ignition switch to
ACC or ON position after at least 2 seconds have elapsed.
If the battery is reconnected with the ignition switch in ACC or ON posi\
tion, or the ignition switch
is turned to ACC or ON within 2 seconds of connecting the battery, it is possible that the diagnosis
system will not operate normally.
 DIAGNOSTIC TROUBLE CODE CHART
Proceed to the appropriate flow chart in step  in accordance with the malfunction code found in step 
or .
 CIRCUIT INSPECTION \b REPAIR
Find out if the problem lies in a sensor, actuator or TROUBLESHOOTING, and repair the problem. After
the problem part is repaired, reinstall the disassembled parts. Do not s\
tart work until at least 90 seconds
after the ignition switch is turned to the LOCK position and the negative (±\
) terminal cable is disconnected.
CAUTION: If incorrect procedure is used, a malfunction may occur in the system o\
r there is the dan-
ger that airbag may be accidentally deploy during the repair operation. \
Carefully read the GENERAL
DESCRIPTION (See page RS±2) and the cautions for each operation, and perform repairs in the cor-
rect order using the correct methods.
HINT: The following illustration for the CIRCUIT INSPECTION shows each conne\
ctor for the SRS squib
circuit.
 
















 
















 
















±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±55
WhereEverybodyKnowsYourName

HINT:

When the SRS warning light remains lit up and the diagnostic trouble code in\
the normal code, this means a
source voltage drop.
This malfunction is not stored in memory by the center airbag sensor assembl\
y and if the power source voltage
returns to normal, after approx. 10 seconds the SRS warning light will automati\
cally go out.

Code 22 in recorded when a malfunction occurs in the SRS warning light syste\
m. If an open malfunction occurs
in the SRS warning light system, the SRS warning light does not light up\
. so that until the malfunction is repaired,
the diagnostic trouble codes (including code 22) cannot be confirmed.

When 2 or more codes are indicated, the lowest numbered code will appear\
first.

If a code not listed on the chart is displayed, then the center airbag s\
ensor assembly is faulty.
RS±62
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
WhereEverybodyKnowsYourName

SYMPTOM SIMULATION
ªIntermittent troubles or problemsº are the malfunctions about which the customer \
has a complaint, but which
do not occur and can not be confirmed in the workshop. The intermittent pr\
oblems also include complaints about
the SRS warning light going on and off erratically.
The self±diagnostic system stores the circuit of the intermittent pro\
blem in memory even if the ignition switch
is turned off.
And, for accurate diagnosis of the problems, ask the customer to obtain info\
rmation as much as possible follow-
ing the customer problem analysis check sheet (See page RS±58) and try to reproduce the intermittent problem.
The problem simulation methods described below are the effective ways for this nature of problem to produce
the problem conditions by applying vibration, heat, and humidity.
1VIBRATION METHOD: When vibration seems to be the major cause.
CONNECTORS
Slightly shake the connector vertically and horizontally.
(Inspection of connectors)
(a) Does the wire harness connecting with its corre-
sponding part have insufficient slack?
(b) Are the terminals dirty?
(c) Are the terminals making loose contact due to termi-
nals spread?
WIRE HARNESS
Slightly shake the wire harness vertically and horizontal-
ly. The connector joint, fulcrum of the vibration, and
body through portion are the major areas to be checked
thoroughly.
PARTS AND SENSORS
Apply vibration slightly by a finger to the part or sensor
considered to be the problem cause and check if the
malfunction will occur.
Caution: Do not apply vibration to the center
airbag sensor assembly.
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±65
WhereEverybodyKnowsYourName