1991 LEXUS SC400 sensor

Circuit Inspection
Diag. Code (Normal)Source Voltage Drop
CIRCUIT DESCRIPTION
The airbag system is equipped with a voltage±increase circuit (DC±DC\
converter) in the center airbag
sensor assembly in case the source voltage drops.
When the battery voltage drops, the voltage±increase circuit (DC±DC c\
onverter) functions to increase
the voltage of the airbag system to normal voltage.
The diagnosis system malfunction display for this circuit is different to other circuits±when the airbag
warning light remains lit up and the diagnostic code is a normal code, source voltage d\
rop is indicated.
Malfunction in this circuit is not recorded in the center airbag sensor assembly, and approx. 10 se-
conds after the source voltage returns to normal, the airbag warning lig\
ht automatically goes off.
Code No.
Diagnosis
(Normal)Source voltage drop.
DIAGNOSTIC CHART
Preparation.
Does airbag warning light turn on after
approx. 10 seconds?
Check battery and charging system
(See page CH±1). Check diagnostic code, and if a
malfunction code is output,
perform troubleshooting according
to malfunction code.
If a normal code is output,
replace center airbag sensor
assembly.
WIRING DIAGRAM
AB±40SRS AIRBAG
± Troubleshooting
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(1) Turn ignition switch LOCK.
(2) Disconnect center airbag sensor assemblyconnector.
(3) Turn ignition switch ON. But do not start engine.
(4) Measure voltage at IG
2 or ACC on connector
wire harness side of center airbag assembly and
operate electric system (defogger, wiper,
headlight, heater, blower, etc.).
Voltage: 6 V ± 11.5 V at IG
2 and ACC.
(5) Turn electric system switch OFF.
(6) Turn ignition switch LOCK.
(7) Remove voltmeter and connect center airbag sensor assembly.
Does airbag warning light turn off after approx. 10 seconds?
Preparation.
Turn ignition switch ON.
Operate electric system checked in [ 1 ] (4) and
check that airbag warning light goes off after
approx. 10 seconds.
Check diagnostic code, and if a malfunction
code is output, perform troubleshooting
according to malfunction code. If a normal
code is output, replace center airbag
sensor assembly.
Check battery and charging system
(See page CH±1)
INSPECTION PROCEDURE
AB±41SRS AIRBAG ± Troubleshooting
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Diag. Code 11Short is Squib Circuit or Front Airbag
Sensor Circuit (to Ground)
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 11 is recorded when occurrence of ground short is detected in the squib circui\
t or front
airbag sensor circuit.
Code No.
Diagnosis
11

Short circuit in squib wire harness (to ground).

Squib malfunction.

Short circuit in front airbag sensor +S wire harness (to ground).

Front airbag sensor malfunction.

Short circuit between +S wire harness and ±S wire harness of front ai\
rbag sensor.

Spiral cable malfunction.

Center airbag sensor assembly malfunction.
DIAGNOSTIC CHART
Preparation.
Check front airbag sensor circuit.
(Measure resistance between terminals +SR
and ±SR, +SL and ±SL of center airbag
sensor assembly connector.
Check front airbag sensor circuit.
(Measure resistance between terminals +SR,
+SL of center airbag sensor assembly
connector and body ground.
Check squib circuit.
Check center airbag sensor assembly.
Check squib.
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. Go to step [ 7 ] on next page.
Repair or replace harness or
connector between center airbag
sensor assembly and front airbag
sensor (See page
AB±20).
Go to step [ 8 ] on next page.
Replace center airbag sensor
assembly.
Replace steering wheel pad.
AB±42SRS AIRBAG ± Troubleshooting
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DIAGNOSTIC CHART (Cont'd)
Check front airbag sensor.Replace front airbag sensor.
Repair or replace spiral cable.Check spiral cable. Repair or replace harness or connector
between center airbag sensor assembly and
front airbag sensor (See page AB±20).
Repair or replace harness or connector
between center airbag sensor assembly and
spiral cable.
WIRING DIAGRAM
AB±43SRS 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±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
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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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