LEXUS SC400 1991 Service Repair Manual

OKNG
OKNG
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.
9Check 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.
Repair or replace harness or connector between center airbag sensor assembly a\
nd front airbag sen-
sor (See page RS±48).
10Check spiral cable.
C
OK
PDisconnect connector between center airbag sensor
assembly and spiral cable.
Measure resistance between D+, D± on spiral cable
side of connector between spiral cable and steering
wheel pad and body ground.
Resistance: 1 M
or Higher
Repair or replace spiral cable.
Repair or replace harness or connector between
center airbag sensor assembly and spiral cable.
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±77
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WIRING DIAGRAM
DTC12
wShort in Squib Circuit of Front Airbag Sensor Circuit
(to B+)
w Open in Front Airbag Sensor Circuit
CIRCUIT DESCRIPTION
The squib circuit consists of the center airbag sensor assembly, spiral cable and the steering wheel pad (squib).
It causes the SRS to deploy when the SRS deployment conditions are satisfi\
ed.
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 12 is recorded when a B+ short is detected in the squib circuit or\
the front airbag sensor circuit.
DTC No.Diagnosis
12
 Short circuit in squib wire harness (to B+)
 Squib malfunction
 Short circuit in front airbag sensor +S wire harness (to B+)
 Open circuit in RH and LH front airbag sensor harness.
 Spiral cable malfunction
 Center airbag sensor assembly malfunction
RS±78±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
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DIAGNOSTIC CHART
(See page RS±48).
(See page
RS±49).
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±79
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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
front 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
± 855

Go to code 15.
RS±80
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OKNG
OKNG
3Check front airbag sensor circuit. (Measure voltage between terminals +SR or\
+SL of center
airbag sensor assembly connector and body ground.)
C
OK
P1. Connect negative (±) terminal cable to battery.
2. Turn ignition switch ON.
Measure voltage between terminals +SR or +SL of har-
ness side connector of center airbag sensor assembly
and body ground.
Voltage: Below 1 V
Repair or replace harness or connector between center
airbag sensor assembly and front airbag sensor (See
page RS±48 ).
4Check D squib circuit.
C
OK
PDisconnect center airbag sensor assembly connector.
Measure resistance voltage between D+ and D± on spi-
ral cable side of connector between spiral cable and
steering wheel pad.
Voltage: Below 1 V
Go to step 
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±81
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OKNG
OKNG
5Check P squib circuit.
C
OK
Measure voltage at P+ on spiral cable side of connector
between spiral cable and steering wheel pad.
Voltage: Below 1 V
Go to step

6Check center airbag sensor assembly.
C
OK
Hint
P1. Turn ignition switch LOCK.
2. Disconnect negative (±) terminal cable from bat-
tery.
3. Connect connector to center airbag sensor assem- bly.
4. Using a service wire, connect D
+ and D± on spiral
cable side connector between spiral cable and
steering wheel pad.
5. Using a service wire, connect P
+ and P± on center
airbag sensor assembly side of connector between
center airbag sensor assembly a dn front passen-
ger airbag assembly.
6. Connect negative (±) terminal cable to battery, and wait at least 2 seconds.
1. Turn ignition switch ACC 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, an s 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 12 is not output.
Code other than code 12 may be output at this time, but
this is not relevant to this check.
Replace center airbag sensor assembly.
RS±82
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SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
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OKNG
OKNG
7Check D squib.
C
OK
Hint
P1. Turn ignition switch LOCK.
2. Disconnect battery negative (±) terminal cable, andwait at least 90 seconds.
3. Connect steering wheel pad (squib) connector.
4. Connect negative (±) terminal cable to battery, and wait at least 2 seconds.
1. Turn ignition switch ACC 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 12 is not output.
Codes other t han code 12 may be output at this time, but
is not relevant to this check.
Replace steering wheel pad.
8Check P squib.
C
OK
Hint
P1. Turn ignition switch LOCK.
2. Disconnect battery negative (±) terminal cable, and
wait at least 90 seconds.
3. Connect front passenger airbag assembly (squib) connector.
4. Disconnect steering wheel pad (squib) connector.
5. Connect negative (±) terminal cable to battery, and wait at least 2 seconds.
1. Turn ignition switch ACC 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.
4. Check diagnostic trouble code.
Diagnostic trouble code 12 is not output.
Codes other t han code 12 may be output at this time, but
they are not relevant to this check.
Replace center airbag sensor assembly.
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±83
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OKNG
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.
9Check spiral cable.
C
OK
P1. Turn ignition switch LOCK.
2. Disconnect connector between center airbag sen-sor assembly and spiral cable.
3. Turn ignition switch ON.
Measure voltage at D+ on spiral cable side of connector
between spiral cable and steering wheel pad.
Voltage: Below 1 V
Repair or replace spiral cable.
Repair or replace harness or connector between center airbag sensor asse\
mbly and spiral cable.
RS±84±
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DTC13Short in Squib Circuit (Between D+ Wire Harness
and D
± Wire Harness
CIRCUIT DESCRIPTION
The squib circuit consists of the center airbag sensor assembly, spiral cable and the steering wheel pad (squib).
It causes the SRS to deploy when the SRS deployment conditions are satisfi\
ed.
For details of the function of each component, see FUNCTION OF COMPONENT\
S on page RS±10.
Diagnostic trouble code 13 is recorded when a short is detected in the D+ wire harn\
ess and D wire harness of
the squib circuit.
DTC No.Diagnosis
13
 Short circuit between D+ wire harness and D± wire harness of squib.
 Squib malfunction.
 Spiral cable malfunction.
 Center airbag sensor assembly malfunction.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±85
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WIRING DIAGRAM
DIAGNOSTIC CHARTDIAGNOSTIC CHART
RS±86±
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