LEXUS SC300 1991 Service Repair Manual

DTC15Open in Front Airbag Sensor Circuit
CIRCUIT DESCRIPTION
The front airbag sensor detects the deceleration force in a frontal collisi\
on and is located in the front fender on
the left and right sides.
For details of the function of each component, see FUNCTION OF COMPONENTS o\
n page RS±10. Diagnostic
trouble code 15 is recorded when an open is detected in the front airbag sensor\
circuit.
NOTICE: The front airbag sensor connector is equipped with an electrical connec\
tion check mechanism
for the purpose of detecting an open in the front airbag sensor (See pa\
ge RS±13). This mechanism is
constructed so that when the terminals of the front airbag sensor have been connect\
ed (when the con-
nector housing lock is in the locked condition), the connection detection pin\
on the wire harness side
connects with the terminals for diagnosis use on the sensor side. If the connector is \
not properly con-
nected, the diagnosis system may detect only a malfunction code, even though the supplemental re-
straint system is functioning normally. When connecting the front airbag sensor connector, make sure
it is connected properly. If diagnostic trouble code 15 is displayed after the front airbag sens\
or connec-
tor has been connected, check again that it is properly connected.
DTC No.Diagnosis
15
 Open circuit in +S wire harness or ±S wire harness of front airbag se\
nsor.
 Front airbag sensor malfunction.
 Malfunction of electrical connection check mechanism of front airbag sen\
sor.
 Center airbag sensor assembly malfunction.
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±97
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WIRING DIAGRAM
DIAGNOSTIC CHARTDIAGNOSTIC CHART
(See page RS±49).
(See page RS±49).
RS±98±
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OKNG
INSPECTION PROCEDURE
1Preparation.
P1. Disconnect battery negative (±) terminal cable, andwait at least 90 seconds.
2. Remove steering wheel pad (See page RS±19).
3. Disconnect connectors of front passenger airbag assembly (See page RS±32).
Caution: Store the steering wheel pad with the
surface facing upward.
2Check front airbag sensor circuit (Measure resistance between terminals +SR \
and ±SR, +SL
and ±SL of center airbag sensor assembly connector.)
C
OK
PDisconnect center airbag sensor assembly connector.
Measure resistance between terminals +SR and ±SR,
+SL and ±SL of harness side connector of center airbag
sensor assembly.
Resistance: 755
± 885

Go to step
.
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±99
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OKNG
3Check center airbag sensor assembly.
C
OK
Hint
P1. Connect connector to center airbag sensor assem-bly.
2. Using a service wire, connect D+ and D± on spiral cable side of connector between spiral cable and
steering wheel pad.
3. Using a service wire, connect P+ and P±n on center
airbag sensor assembly side of connector between
center airbag sensor assembly and front passen-
ger airbag.
4. Connect negative (±) terminal cable to battery, and wait at least 2 seconds.
1. Turn ignition switch AAC or ON, and wait at least 20 seconds.
Clear malfunction code. Turn ignition switch LOCK
and wait at least 20 seconds.
2. Turn ignition switch ACC or ON, and wait at least 20
seconds.
3. Using SST, connect terminals Tc and E
1 of DLC2.
SST 09843±18020
4. Check diagnostic trouble code.
Diagnostic trouble code 15 is not output.
Code other than code 15 may be output at this time, but
this is not relevant to this check.
Replace center airbag sensor assembly.
From the results of the above inspection, the malfunctioning part can now be\
considered normal. To
make sure of this, use the simulation method to check.
RS±100±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
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OKNG
OKNG
4Check front airbag sensor.
C
OK
PDisconnect front airbag sensor connector.
Measure resistance between each terminal of front air-
bag sensor.
Notice:
Do not touch ohmmeter probes strongly against
terminals of front airbag sensor.
 Make sure the front airbag sensor connector is
properly connected.
Replace front airbag sensor.
5Check harness between center airbag sensor assembly and front airbag sen\
sor.
C
OK
P5. Disconnect center airbag sensor assembly con- nector.
6. Using service wires, connect +SR and ±SR, +SL and ±SL on the wire harness side of the center air-
bag sensor assembly connector.
Measure resistance between terminals +SR and ±SR,
+SL and ±SL of harness side connector of front airbag
sensor.
Notice:
 Lightly t ouch ohmmeter proves at position shown
in illustration.
 Make sure the front airbag sensor connector is
properly connected.
Resistance: Below 1

Repair or replace harness or connector between center
airbag sensor assembly and front airbag sensor. (See
page RS±48 ).
Replace front airbag sensor connector (See page RS±48).
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±101
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DTC22SRS Warning Light System Malfunction
CIRCUIT DESCRIPTION
The SRS warning light is located on the combination meter.
When the supplemental restraint system is normal, the SRS warning light ligh\
ts up for approx. 6 seconds after
the ignition switch is turned from LOCK position to ACC or ON position, and then turn\
s off automatically. If there
is a malfunction in the supplemental restraint system, the SRS warning l\
ight lights up to inform the driver of the
abnormality.
When terminals Tc and E
1 of the DLC2 are connected, the diagnostic trouble code is displayed by the blinking
of the SRS warning light.
The SRS warning light circuit is equipped with an electrical connection che\
ck mechanism which detects when
the connector to the center airbag sensor assembly is not properly connecte\
d.
If the connector to the center airbag sensor assembly is not properly conn\
ected, the SRS warning light will not
light up.
Diagnostic trouble code 22 is recorded when a malfunction occurs in the SRS warnin\
g light system. 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 22) c\
annot be confirmed.
DTC No.Trouble Area
22 Open circuit in SRS warning light system.
 Center airbag sensor assembly malfunction.
RS±102±
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DIAGNOSTIC CHART
DIAGNOSTIC
CHART
Troubleshooting for this system is different for when the SRS warning light does not light up and for when dia\
g-
nostic trouble code 22 is output. Confirm the problem symptoms first before selecting the appropriate trouble-
shooting procedure.
HINT: If SRS warning light does not light up, perform the following troubles\
hooting:
(See page RS±65)
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±103
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WIRING DIAGRAM
DIAGNOSTIC CHARTDIAGNOSTIC CHART
HINT: If diagnostic trouble code 22 is output, perform the following troubles\
hooting:
(See page RS±65).
RS±104±
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OKNG
OKNG
INSPECTION PROCEDURE
HINT: If SRS warning light does not light up, perform the following troublesh\
ooting:
1Check ECU±B fuse.
Go to step

2Preparation.
P1. Disconnect battery negative (±) terminal cable, and
wait at least 90 seconds.
2. Remove steering wheel pad (See page RS±19).
3. Disconnect connectors of front passenger airbag assembly (See page RS±32).
Caution: Store the steering wheel pad with the
surface facing upward.
3Check connection of center airbag sensor assembly connector.
Repair.
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±105
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OKNG
YESNO
YESNO
4Check SRS warning light circuit.
C
OK
P1. Disconnect center airbag sensor assembly.
2. Connect negative (±) terminal cable to battery.
3. Turn ignition switch ACC or ON.
Measure voltage LA terminal of harness side connector
of center airbag sensor assembly.
Voltage: Battery positive voltage.
Repair SRS warning light circuit.
5Does SRS warning light come on?
C
OK
P1. Disconnect negative (±) terminal cable from bat-tery.
2. Connect center airbag sensor assembly.
3. Connect negative (±) terminal cable to battery.
4. Turn ignition switch ACC or ON.
Check operation of SRS warning light.
SRS warning light comes on.
Check terminal LA of center airbag sensor assembly and
electrical connection check mechanism. If normal, re-
place center airbag sensor assembly.
From the results of the above inspection, the malfunctioning part can now be\
considered normal. To
make sure of this, use the simulation method to check.
6Is new ECU±B fuse burnt out again?
Using simulation method, reproduce malfunction symp-
toms (See page RS±65).
Check harness between ECU±B fuse and SRS warning light, and ECU±B fuse a\
nd center airbag sensor
assembly.
RS±106±
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