ignition switch LEXUS SC400 1991 Service Owner's Manual

Check voltage between terminals MGC of air conditioner control assem-
bly connector and body ground.
(1) Remove console upper panel.(See page BO-111 ).
(2) Remove A/C control assembly with connec±
tors still connected.
(3) Start the engine.
Check voltage between terminals MGC of air condi-
tioner control assembly connector and body ground
when magnetic clutch is on and off by A/C
switch.
Go to step (7).
Check voltage between terminals MGC of air conditioner control assem-
bly harness side connector and body ground.
(1) Disconnect air conditioner control assemblyconnector.
(3) Turn ignition switch ON.
Check voltage between terminals MGC of air condi-
tioner control assembly harness side connector and
body ground.
Voltage: 4 ± 6 V
Check and replace air conditioner control
assembly.
Check for open and short in harness and connector between
air conditioner control assembly and engine & ECT ECU (See page IN-27).
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
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AIR CONDITIONING SYSTEM TroubleshootingAC±87
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Check magnetic clutch relay.
Remove magnetic clutch relay from R/B No. 2
Check continuity between each pair of terminals
shown below of magnetic clutch relay.
(1) Apply battery voltage between terminals 2 and 3
(2) Check continuity between terminals 4 and 1
Replace magnetic relay.
(1) Remove engine & ECT ECU with connectors still connected.
(2) Turn ignition switch ON.
(1) Push one of the fan speed control switches
(Lo, Med or Hi).
(2) Measure voltage between terminal ACMG of engine & ECT ECU connector and body
ground.
Go to step (10).
Check voltage between terminal ACMG of engine & ECT ECU and
body ground.
Check for open and short in harness and connector between engine &
ECT ECU and battery (See page IN-27).
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
Check for open and short in harness and connector between air conditioner control
assembly and compressor relay, compressor relay and battery (See page IN-27).
Repair or replace harness or connector.
Check and replace air conditioner control a ssembly.
AC±88±
AIR CONDITIONING SYSTEM Troubleshooting
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Check voltage between terminal SET 1 ~ 5 and SG of A/C control
assembly
(1) Remove A/C control assembly with connec-tors.(See page AC-138).
(2) Turn ignition switch ON.
Measure voltage between terminals SET 1 ~ 5 and
SG of temp. control switch is turned from most left to
right position.
for USA spec.for Canada spec.
Proceed to next circuit inspection shown on
matrix chart. ( See page AC-36).
Go to step (2).
INSPECTION PROCEDURE
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AIR CONDITIONING SYSTEM TroubleshootingAC±93
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Check voltage between terminal SAUTO and SG of A/C control
assembly.
(2) Remove A/C control assembly with connectorsstill connected.
Proceed to next circuit inspection shown on
matrix chart. ( See page AC-36).
(3) Turn ignition switch on.
(1) Remove console upper panel. (See page
BO±111 ).
Measure voltage between terminal SAUTO and Sg
of A/C control assembly when automatic control SW
is operated.
Disconnect automatic control switch connector.
Measure resistance between terminal and of auto-
matic control switch connector when it is is
operated.
Replace automatic control switch.
Check automatic control switch.
Check for open and short in harness and connector between switch and
A/C control assembly (See page IN-27).
Repair or replace harness or connector.
Check and replace A/C control assembly.
INSPECTION PROCEDURE
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AIR CONDITIONING SYSTEM TroubleshootingAC±97
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Check voltage between terminal Tc and E1 of TDCL.
(2) Check voltage between terminals Tc and E1 of TDCL.
Voltage: 10 ± 14 V
(1) Turn ignition switch on.
Proceed to next circuit inspection shown on
matrix chart. ( See page AC-36).
Check for open and short in harness and connector between air conditioner con-
trol assembly and TDCL, TDCL and body ground.(See page IN-27).
Repair or replace harness or connector.
Check and replace air conditioner control
assembly.
INSPECTION PROCEDURE
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AIR CONDITIONING SYSTEM TroubleshootingAC±99
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Check center airbag sensor assembly.
Diagnostic code 14 is not output.(1) Connect connector to center airbag sensor
connector.
(2) Connect connector between center airbag sensor assembly and spiral cable.
(3) Using a service wire, connect D+ and D± on spiral cable side of connector between spiral
cable and steering wheel pad.
(4) Connect negative (±) terminal cable to battery,
and wait at least 2 seconds.
Check squib.
(1) Turn ignition switch ACC or ON, and wait at least 20 seconds.
(2) Using SST, connect terminals Tc and E1 of TDCL.
SST 09843±18020
(3) Check diagnostic code.
(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.
Diagnostic code 14 is not output. (1) Turn ignition switch ACC or ON, and wait at least 20 seconds.
(2) UsingSST, connect terminals Tc and E1 of TDCL.
SST 09843±18020
(3) Check diagnostic code. Codes other than code 14 may be output at this
time, but this is not relevant to this check
Codes other than code 14 may be output at this
time, but this is not relevant to this check Replace steering wheel pad.
From the results of the above inspection, the malfunctioning part can no\
w be considered normal.
To make sure this, use the simulation method to check. Replace center airbag sensor assembly.
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3
Codes other than code 15 may be output at this
time, but this is not relevant to this check.Replace front airbag sensor.
NG
OK
(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.
Check center airbag sensor assmbly.
Check front airbag sensor.
Replace center airbag sensor assembly.NG
OK
Diagnostic code 15 is not output.
(1) Connect connector to center airbag sensor
assembly.
(2) Using a service wire, connect D+ and 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.
From the results of the above inspection, the malfunctioning part can no\
w be considered normal.
To make sure of this, use the simulation method to check.
4
Disconnect front airbag sensor connector. Measure resistance between each terminal of
front airbag sensor.

Do not touch ohmmeter probes strongly
against terminals of front airbag sensor.

Make sure the front airbag sensor connector
is properly connected.
Terminal Resistance
Below 1 
755
 ±885 
1 M or higher
+S ± +A
+S ± ±S
±S ± ±A
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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.
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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±
SRS AIRBAG Troubleshooting
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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\
:
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