1991 LEXUS SC400 sensor

5Check harness between center airbag sensor assembly and front airbag
sensor.
(1) Disconnect center airbag sensor assembly
connector.
(2) Using service wires, connect +SR and ±SR, +SL and ±SL on the wire harness side of the
center airbag sensor assembly connector.
Measure resistance between terminals +SR and
±SL, +SL and ±SL of harness side connector of
front airbag sensor.

Lightly touch ohmmeter probes at
position shown in illustration.

Make sure the front airbag sensor con-
nector is properly connected.
Repair or replace harness or connector between
center airbag sensor assembly and front airbag
sensor (See page AB±20).
Replace front airbag sensor connector (See page AB±20)
NG
OK
Resistance: Below 1

AB±72±
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Diag. Code 22Airbag Warning Light System Malfunction
CIRCUIT DESCRIPTION
The airbag warning light is located on the combination meter.
When the airbag system is normal, the airbag warning light lights up for\
approx. 6 seconds after the
ignition switch is turned from LOCK position to ACC or ON position, and then turns off automatically.
If there is a malfunction in the airbag system, the airbag warning light\
lights up to inform the driver of
the abnormality.
When terminals Tc and E of the TDCL are connected, the diagnostic code is displayed by t\
he blinking
of the airbag warning light.
The airbag warning light circuit is equipped with an electrical connecti\
on check mechanism which
detects when the connector to the center airbag sensor assembly is not p\
roperly connected.
If the connector to the center airbag sensor assembly is not properly co\
nnected, the airbag warning
light will not light up.
Diagnostic code 22 is recorded when a malfunction occurs in the airbag w\
arning light system.
If an OPEN malfunction occurs in the airbag warning light system, the ai\
rbag warning light does not
light up, so that until the malfunction is repaired, the diagnostic code\
s (including code 22) cannot be
confirmed.
Code No.Diagnosis
22
Open circuit in airbag warning light system.22
Center airbag sensor assembly malfunction.
AB±74±
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OKNG
1
2
3
4
5
6
6
OK
OK
YES
YES NG
NG NO
NO
Check connection of center airbag sensor
assembly connector.
Preparation.
Check airbag warning light circuit.
Does airbag warning light come on?
Is new ECU ±B fuse burnt out again? GO to step
Repair.
Repair airbag warning light circuit
(See page BE±150).
Check terminal LA of center
airbag sensor assembly and
electrical connection check
mechanism. If normal, replace
center airbag sensor assembly.
Using simulation method,
reproduce malfunction symptoms
(See page IN±20).
Check harness between ECU ±B fuse and
airbag warning light, and ECU±B fuse and
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.
Check ECU ±B fuse.
DIAGNOSTIC CHART
Troubleshooting for this system is different for when the airbag warning light does not light up and for
when diagnostic code 22 is output. Confirm the problem symptoms first before\
selecting the appropriate
troubleshooting procedure.
HINT: If airbag warning light does not light up, perform the following troub\
leshooting:
±
SRS AIRBAG TroubleshootingAB±75
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YESNO
1
Replace center airbag sensor assembly. Using simulation method,
reproduce malfunction symptoms
(See page
IN±20).
WIRING DIAGRAM
Is diagnostic code 22 output again?
DIAGNOSTIC CHART
HINT: If diagnostic code 22 is output, perform the following troubleshooting:\
AB±76
±
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Check ECU±B fuse.
NG
OK
1
6Go to step
(1) Disconnect battery negative (±) terminal cable, and wait at least 20 seconds.
(2) Remove steering wheel pad (See page AB±14).
When storing steering wheel pad, keep upper
surface of pad facing upward.
NG
OKRepair.
Check connection of center airbag sensor assembly connector.2
3Preparation.
INSPECTION PROCEDURE
HINT: If airbag warning light does not light up, perform the following troubl\
eshooting:
±
SRS AIRBAG TroubleshootingAB±77
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4
5
6
Check terminal LA of center airbag sensor assem-
bly and electrical connection check mechanism.
If normal, replace center airbag sensor assembly.
NG
OK
(1) Disconnect negative (±) terminal cable from battery.
(2) Connect center airbag sensor assembly.
(3) Connect negative (±) terminal cable to battery.
(4) Turn ignition switch ACC or ON. Voltage: 10±14 V
Check operation of airbag warning light.
(1) 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.
Repair airbag warning light circuit
(see page BE±150).
NG
Using simulation method, reproduce
malfunction symptoms (See page In±20).NG
OK
Check airbag warning light circuit.
Does airbag warning light come on?
Is new ECU±B fuse burnt out again?
From the results of the above inspection, the malfunctioning part can now be considered norm\
al. To
make sure of this, use the simulation method to check.
Check harness between ECU±B fuse and airbag warning light, and ECU±B fus\
e and center airbag sensor
assembly.
AB±78±
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1
Using simulation method, reproduce malfunction
symptoms (See page IN±20).NO
YES
(1) Turn ignition switch LOCK, and wait at least 2
seconds.
(2) Turn ignition switch ACC or ON, and wait at least 20 seconds.
(3) Using SST, connect terminals Tc and E
1 of TDCL.
SST 09843±18020
(4) Check diagnostic code. Clear malfunction code 41 stored in memory
(See page
AB±35).
Is diagnostic code 22 output again?
Replace center airbag sensor assembly.
HINT: If diagnostic code 22 is output, perform the following troubleshooting\
:
±
SRS AIRBAG TroubleshootingAB±79
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YES
Is diagnostic code 31 output again?
NO
1
Replace center airbag sensor assembly. Using simulation method, reproduce
malfunction symptoms
(See page
IN±20).
Diag. Code 31Center Airbag Sensor Assembly Malfunction
CIRCUIT DESCRIPTION
The center airbag sensor assembly consists of a center airbag sensor, safing sensors, ignition control
and drive circuit, diagnosis circuit, etc.
It receives signals from the airbag sensors, judges whether or not the a\
irbag must be activated, and
diagnoses system malfunction.
Diagnostic code 31 is recorded when occurrence of a malfunction in the center airba\
g sensor assembly
is detected.
Code No.Diagnosis
31 Center airbag sensor assembly malfunction.
DIAGNOSTIC CHART
HINT: When a malfunction code other than code 31 is displayed at the same tim\
e, first repair the
malfunction indicated by the malfunction code other than code 31.
AB±80
±
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