1991 LEXUS SC400 wiring diagram

Preperation.
Check squib circuit.
Check spiral cable.Check harness between center airbag
sensor assembly and spiral cable.
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 simula-
tion method to check. Go to step
Repair or replace spiral cable.
Repair or replace harness or con-
nector between center airbag sen-
sor assembly and spiral cable. Replace center airbag
sensor assembly
Replace steering wheel pad.
WIRING DIAGRAM
DIAGNOSTIC CHARTDIAGNOSTIC CHART
±
SRS AIRBAG TroubleshootingAB±63
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Preperation.
Check front airbag sensor circuit.
(Measure resistance between terminals +SR
and ±SR, +SL and ±SL of center airbag sen-
sor assembly connector.)
Check center airbag sensor assembly.From the results of the above inspection, the
malfunctioning part can now be considered nor-
mal. To make sure of this, use the simulation
method to check.
Check front airbag sensor.
Check harness between center airbag
sensor assembly and front airbag sensor.
Replace front airbag sensor connector
(See page AB±20). Replace center airbag sensor
assembly. Go to step
Replace front airbag sensor.
Repair or replace harness or con-
nector between center airbag sen-
sor assembly and front airbag sen-
sor (See page AB±20).
WIRING DIAGRAM
DIAGNOSTIC CHARTDIAGNOSTIC CHART
±
SRS AIRBAG TroubleshootingAB±69
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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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OK
Check operation of airbag warning light.
NG1
WIRING DIAGRAM
2Is diagnostic code 41 output again? System is normal.
Check harness between ECU±B
fuse and center airbag sensor as-
sembly. If normal, replace center
airbag sensor assembly.
Perform troubleshooting according to
malfunction code output. NO
YES
Diag. Code 41Malfunction Stored in Memory
CIRCUIT DESCRIPTION
If a malfunction occurs in the airbag system, malfunction codes 11 to 31 may be output, and when the
battery is disconnected after the malfunction is repaired, malfunction codes 11 to 31 will be cleared,
but code 41 will be output instead.
So long as the cancellation operation for a malfunction stored in memory (\
See page
AB±32) is not per-
formed, code 41 is stored in the center airbag sensor assembly and the airbag w\
arning light remains
lit up.
Code No.Diagnosis
41
Malfunction recorded in memory.41
Center airbag sensor assembly malfunction.
DIAGNOSTIC CHART
AB±82±
SRS AIRBAG Troubleshooting
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YES
Does airbag warning light turn off?
NO
1
Replace center airbag sensor assembly. Check airbag warning light circuit
or terminal AB circuit of TDCL or
check connector.
WIRING DIAGRAM
Airbag Warning Light System (Always Lit Up)
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.
DIAGNOSTIC CHART
AB±84±
SRS AIRBAG Troubleshooting
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WIRING DIAGRAM
DIAGNOSTIC CHART
±
SRS AIRBAG TroubleshootingAB±87
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Wiring Diagram
CENTER AIRBAG SENSOR ASSEMBLY CONNECTOR
No.SymbolTerminal NameNo.SymbolTerminal Name
18E2Ground
2±SRRH Front Airbag Sensor (±)9LAAirbag Warning Light
3+SRRH Front Airbag Sensor (+)10D±Squib (±)
4+SLLH Front Airbag Sensor (+)11D+Squib (+)
5±SLLH Front Airbag Sensor (±)12TcDiagnosis
6+BBattery (ECU±B Fuse)13E1Ground
7IG2Power Source (IGN Fuse)14AccPower Source (CIG Fuse)
AL1Electrical Connection Check
MechanismBL2Electrical Connection Check
Mechanism
AB±33SRS AIRBAG ± Troubleshooting
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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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