LEXUS SC400 1991 Service Repair Manual

Check squib circuit.
Disconnect connector between center airbag sen-
sor 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.
Repair or replace spiral cable.
Repair or replace harness or connector between
center airbag sensor assembly and spiral cable,
Resistance: 1 M
or higher AB±47
SRS AIRBAG
± Troubleshooting
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Diag. Code 12Short in Squib Circuit or Front Airbag
Sensor Circuit (to +B)
CIRCUIT DESCRIPTION
The squib circuit consists of the center airbag sensor assembly, spiral cable and the steering wheel
pad (squib). It causes the airbag to deploy when the airbag deployment\
conditions are satisfied.
The front airbag sensor detects the deceleration force in a frontal collision 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 on page AB±5.
Diagnostic code 12 is recorded when a +B short is detected in the squib circuit or the front airbag
sensor circuit.
Code 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.
AB±48SRS AIRBAG ± Troubleshooting
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DIAGNOSTIC CHART
Preparation.
Check front airbag sensor circuit.
(Measure voltage between terminal +SR
or +SL of center airbag sensor assembly
connector and body ground).
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.
Repair or replace harness or connector
between center airbag sensor assembly and
spiral cable. Check front airbag sensor circuit.
(Measure resistance between terminals +SR
and ±SR, +SL and ±SL of center airbag
sensor assembly connector).
Check squib circuit.
Check center airbag sensor assembly.
Check squib.
Check spiral cable.Repair or replace spiral cable.
Go to step [ 7 ].
Replace center airbag sensor
assembly.
Replace steering wheel pad.
Go to Code 15 (See page
AB±68).
Repair or replace harness or
connector between center airbag
sensor assembly and front airbag
sensor (See page AB±20).
WIRING DIAGRAM
AB±49SRS AIRBAG ± Troubleshooting
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(1) Disconnect battery negative (±) terminal cable,and wait at least 20 seconds.
(2) Remove steering wheel pad (See page AB±14).
Check front airbag sensor circuit. (Measure resistance between terminals +SR\
and
±SR, +SL and ±SL of center airbag sensor assembly connector.
Preparation.
Disconnect center airbag sensor assembly con-
nector.
Measure resistance between terminals +SR and
±SR, +SL and ±SL of harness side connector of
center airbag sensor assembly.
Go to Code 15 (See page AB±68).
When storing steering wheel pad, keep upper
surface of the pad facing upward.
Resistance: 755
± 855

Check front airbag sensor circuit. (Measure voltage between terminal +S\
R or +SL
of center airbag sensor assembly connector and body ground.
(1) Connect negative (±) terminal cable to
battery.
(2) Turn ignition switch ON.
Repair or replace harness or connector
between center airbag sensor assembly
and front airbag sensor (See page AB±20).
Resistance: 1 V
Measure voltage between terminals +SR or +SL
of harness side connector of center airbag sensor
assembly and body ground.
INSPECTION PROCEDURE
AB±50SRS AIRBAG ± Troubleshooting
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(1) Turn ignition switch LOCK.
(2) Disconnect negative (±) terminal cable frombattery.
(3) Connect connector to center airbag sensor assembly.
(4) Using a service wire, Connect D
+ and D± on
spiral cable side of connector between spiral
cable and steering wheel pad.
(5) Connect negative (±) terminal cable to battery, and wait at least 2 seconds.
Check squib circuit.
Codes other than code 12 may be output at this
time, but this is not relevant.
Measure voltage at D+ on spiral cable side of con-
nector between spiral cable and steering wheel
pad.
Go to step [ 7 ].
Resistance: 1 V
Replace center airbag sensor assembly.
Check center airbag sensor assembly.
(1) Turn ignition switch ACC or ON and wait at least 20 seconds.
(2) Using SST, connect terminals Tc and E
1 of
TDCL.
SST 09843±18020
(3) Check diagnostic code.
Diagnostic code 12 is not output. AB±51
SRS AIRBAG
± Troubleshooting
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(1) Turn ignition switch LOCK.
(2) Disconnect battery negative (±) terminal cable,and wait at least 20 seconds.
(3) Connect steering wheel pad (squib) connector.
(4) Connect negative (±) terminal cable to battery, and wait at least 2 seconds.
Check squib.
Measure voltage at D+ on spiral cable side of con-
nector between spiral cable and steering wheel
pad.
Repair or replace spiral cable.
Diagnostic code 12 is not output.
Replace steering wheel pad.
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.
Repair or replace harness or connector between center airbag sensor assembly a\
nd spiral cable.
Check spiral cable.
(1) Turn ignition switch ACC or ON, and wait at least 20 seconds.
(2) Using SST, connect terminals Tc and E
1 of
TDCL.
SST 09843±18020
(3) Check diagnostic code.
Codes other than code 12 may be output at this
time, but this is not relevant.
Voltage: Below 1 V
(1) Turn ignition switch LOCK.
(2) Disconnect connector between center airbag sensor assembly and spiral cable.
(3) Turn ignition switch ON.
AB±52
SRS AIRBAG
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MEMOAB±53
SRS AIRBAG
± Troubleshooting
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Diag. Code 13Short 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 airbag to deploy when the airbag deployment\
conditions are satisfied.
For details of the function of each component, see FUNCTION OF COMPONENT\
S on page AB±7.
Diagnostic code 13 is recorded when a short is detected in the D+ wire harness and\
D± wire harness
of the squib circuit.
Code 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 CHART
Preparation.
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.
Check squib circuit.
Check center airbag sensor assembly.
Check squib.
Go to step [ 5 ] on next page.
Replace center airbag sensor
assembly.
Replace steering wheel pad.
AB±54SRS AIRBAG ± Troubleshooting
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DIAGNOSTIC CHART (Cont'd)
Check spiral cable.Repair or replace spiral cable.
Check harness between center airbag
sensor assembly and spiral cable.Repair or replace harness or
connector between center airbag
sensor assembly and spiral cable.
Check center airbag sensor assembly.Replace center airbag sensor
connector.
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.
WIRING DIAGRAM
AB±55SRS AIRBAG ± Troubleshooting
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INSPECTION PROCEDURE
(1) Disconnect battery negative (±) terminal cable,and wait at least 20 seconds.
(2) Remove steering wheel pad (See page AB±14).
Preparation.
Measure resistance between D+ and D± on spiral
cable side of connector between spiral cable and
steering wheel pad.
Go to step [ 5 ].
When storing steering wheel pad, keep upper
surface of the pad facing upward.
Resistance: 1 k
or higher
Check squib circuit.
AB±56SRS AIRBAG ± Troubleshooting
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