1991 LEXUS SC400 airbag

(1) Disconnect battery negative (±) terminal cable,and wait at least 20 seconds.
(2) Remove steering wheel pad (See page AB±16).
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 step [ 7 ].
When storing steering wheel pad, keep upper
surface of the pad facing upward.
Resistance: 755
± 855

Check front airbag sensor circuit. (Measure resistance between terminals +SR\
and
+SL of center airbag sensor assembly connector and body ground.
Measure resistance between terminals +SR, +SL
of harness side connector of center airbag sensor
assembly and body ground.
Repair or replace harness or connector
between center airbag sensor assembly
and front airbag sensor (See page AB±20).
Resistance: 1 M
or higher
INSPECTION PROCEDURE
AB±44SRS AIRBAG ± Troubleshooting
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(1) Connect connector to center airbag sensorassembly.
(2) Using a service wire, connect D
+, D± on spiral
cable side of connector between spiral cable
and steering wheel pad.
(3) Connect negative (±) terminal cable to battery, and wait at least 2 seconds.
Check squib circuit.
Codes other than code 11 may be output at this
time, but this is not relevant.
Measure resistance between D+, D± on spiral cable
side of connector between spiral cable and steer-
ing wheel pad and body ground.
Go to step [ 8 ].
Diagnostic code 11 is not output.
Resistance: 1 M
or higher
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. AB±45
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.
Disconnect front airbag sensor connector.
Measure resistance between each terminal of
front airbag sensor.
Replace front airbag sensor.
Diagnostic code 11 is not output.
Replace steering wheel pad.
wDo not touch ohmmeter probes strongly against
terminals of front airbag sensor.
w Make sure the front airbag sensor connector is
properly connected.
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 front airbag
sensor (See page AB±20).
Check front airbag sensor.
(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 11 may be output at this
time, but this is not relevant.
AB±46
SRS AIRBAG
± Troubleshooting
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName

(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
WhereEverybodyKnowsYourName

(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
WhereEverybodyKnowsYourName