LEXUS SC400 1991 Service Repair Manual

DIAGNOSTIC TROUBLE CODE MATRIX CHART
If a malfunction code is displayed during the diagnostic trouble code chec\
k, check the circuit listed for that
code in the table below (Proceed to the page given for that circuit).
 DTC No.\
 \
Diagnosis Page
 (Normal)*1\
 \

Source voltage drop RS±68
 11\
 \

Short in squib circuit or front airbag sensor circuit (to ground) RS±70
 12\
 \

Short in squib circuit or front airbag sensor circuit (to B+) RS±78
 13\
 \

Short in squib circuit (between D+ wire harness and D± wire harness\
) RS±85
 14\
 \

Open in squib circuit (between D+ wire harness and D± wire harness)\
 RS±92
 15\
 \

Open in front airbag sensor circuit RS±97
 22*2\
 \

SRS warning light system malfunction RS±102
 31\
 \

Center airbag sensor assembly malfunction RS±108
 53\
 \

Short in squib circuit (between P+ wire harness and P± wire harness\
) RS±110
 54\
 \

Open in squib circuit (between P+ wire harness and P± wire harness)\
 RS±115
HINT:
*
1 When the SRS warning light remains lit up and the diagnostic trouble co\
de is the normal code, this means
a source voltage drop.
*
2 Code 22 is recorded when a malfunction occurs in the SRS warning light \
system. If an open malfunction
occurs in the SRS warning light system, the SRS warning light does not light up, s\
o that until the malfunction
is repaired, the diagnostic trouble code (including 22) cannot be conf\
irmed.
PROBLEM SYMPTOM CHART
Proceed with troubleshooting of each circuit in the table below.
\
 \
Problem Symptom Inspection Item Page
\
 

\



With the ignition switch at ACC or ON, the SRS warning light
sometimes lights up after approx. 6 seconds have elapsed
SRS warning light system
(Always lit upwhen ignition switch isRS±119\
 

\



SRS warning light lights up even when ignition switch is in
the LOCK position (Always lit up when ignition switch is
LOCK position)RS±11 9
\
 \

Diagnostic trouble code not displayed.
Tc terminal circuitRS±121
\
 \

Diagnostic trouble code continuously displayed.
Tc terminal circuitRS±121
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±67
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WIRING DIAGRAM
CIRCUIT INSPECTION
DTC(Normal)Source Voltage Drop
CIRCUIT DESCRIPTION
The supplemental restraint 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\
converter) functions to increase the volt-
age of the supplemental restraint system to normal voltage.
The diagnosis system malfunction display for this circuit is different to other circuits ± when the SRS warning
light remains lit up and the diagnostic trouble code is a normal code, source\
voltage drop is indicated. Malfunc-
tion in this circuit is not recorded in the center airbag sensor assembly, and approx. 10 seconds after the source
voltage returns to normal, the SRS warning light automatically goes off.
DTC No.Diagnosis
(Normal)Source voltage drop.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
(See page CH±1).
RS±68±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
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YESNO
INSPECTION PROCEDURE
1Preparation.
P1. Turn ignition switch LOCK.
2. Disconnect battery negative (±) terminal cable, andwait at least 90 seconds.
3. Connect battery negative (±) terminal cable.
4. Disconnect center airbag sensor assembly con- nector.
5. Turn ignition switch ON. But do not start engine.
6. Measure voltage at IG
2 or ACC on connector wire
harness side of center airbag sensor assembly and
operate electric system (defogger, wiper, headlight,
heater blower, etc.)
Voltage: 6 V ± 11.5 V at IG
2 and ACC.
7. Turn electric system switch OFF.
8. Turn ignition switch LOCK.
9. Disconnect battery negative (±) terminal cable, and wait at least 90 seconds.
10. Remove voltmeter and connect center airbag sen- sor assembly connector.
11. Connect battery negative (±) terminal cable.
2Does SRS warning light turn off after approx. 10 seconds?
C
PTurn ignition switch ACC or ON and wait at least 20 sec-
onds.
Clear malfunction code. Turn ignition switch LOCK and
wait at least 20 seconds.
Operate electric system checked in
(5) and check
that SRS warning light goes off after approx. 10 sec-
onds.
Check diagnostic trouble code, and if a malfunction code
is output, perform trouble shooting according to mal-
function code. If a normal code is output, replace center
airbag sensor assembly.
Check battery and charging system.
(See page CH±1)
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±69
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DTC11Short in Squib Circuit or Front Airbag Sen-
sor Circuit (to Ground)
CIRCUIT DESCRIPTION
The squib circuit consists of the center airbag sensor assembly, spiral cable and the steering wheel pad (squib),
wire harness connector and front passenger airbag assembly (squib). It\
causes the SRS to operate when the
SRS operation conditions are satisfied.
The front airbag sensor detects the deceleration force in a frontal collisi\
on 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 o\
n page RS±10. Diagnostic
trouble code 11 is recorded when occurrence of ground short is detected in the squib ci\
rcuit or front airbag sen-
sor circuit.
DTC No.Diagnosis
11
 Short circuit in squib wire harness (to ground)
 Squib malfunction
 Short circuit in front airbag sensor +S, D
+, D±, P+, P± wire harness (to ground).
 Front airbag sensor malfunctions.
 Short circuit between +S wire harness and ±S wire harness of front ai\
rbag sensor.
 Spiral cable malfunction.
 Center airbag sensor assembly malfunction.
RS±70±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
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DIAGNOSTIC CHART
DIAGNOSTIC
CHART
(See page RS±49).
(See page RS±48).
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±71
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WIRING DIAGRAM
DIAGNOSTIC CHART (Cont'd)DIAGNOSTIC CHART (Cont'd)
(See page RS±49).
RS±72±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
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OKNG
INSPECTION PROCEDURE
1Preparation.
P1. Disconnect battery negative (±) terminal cable, andwait at least 90 seconds.
2. Remove steering wheel pad (See page RS±19).
3. Disconnect connectors of front passenger airbag assembly (See page RS±32).
Caution: Store the steering wheel pad with the
surface facing upward.
2Check front airbag sensor circuit. (Measure resistance between terminals +SR and ±SR, +SL
and ±SL of center airbag sensor assembly connector.)
C
OK
PDisconnect center airbag sensor assembly connector.
Measure resistance between terminals +SR and ±SR,
+SL and ±SL of harness side connector o center airbag
sensor assembly.
Resistance: 755
± 885

Go to step

±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±73
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OKNG
OKNG
3Check front airbag sensor circuit. (Measure resistance between terminals +SR\
and +SL of cen-
ter airbag sensor assembly connector and body ground.)
C
OK
Measure resistance between terminals +SR, +SL of
harness side connector of center airbag sensor assem-
bly and body ground.
Resistance: 1 M
or higher
Repair or replace harness or connector between center
airbag sensor assembly and front airbag sensor (See
page RS±48 ).
4Check D squib circuit.
C
OK
For the connector (on the spiral cable side) between the
spiral cable and steering wheel pad, measure the resist-
ance between D+, D± and body ground.
Resistance: 1 M
or higher
Go to step 
RS±74
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
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OKNG
OKNG
5Check P squib circuit.
OK
PFor the connector (on the center airbag sensor assem-
bly side) between the center airbag sensor assembly
and front passenger airbag assembly, measure the re-
sistance between P+, P± and body ground.
Resistance: 1 M
or Higher
Repair or replace harness or connector between the cen-
ter airbag sensor assembly and front passenger airbag
assembly.
6Check center airbag sensor assembly.
C
OK
Hint
P1. Connect connector to center airbag sensor assem- bly.
2. Using a service wire, connect D+ and D± on spiral cable side of connector between spiral cable and
steering wheel pad.
3. Using a service wire, connect P+ and P± on center airbag sensor assembly and front passenger air-
bag assembly.
4. Connect negative (±) terminal cable to battery, and wait at least 2 seconds.
1. Turn ignition switch ACC or ON and wait at least 20 seconds.
2. Using SST, connect terminals Tc and E
1 of DLC2.
SST 09843±18020
3. Check diagnostic trouble code.
Diagnostic trouble code 11 is not output.
Codes other than code 11 may be output at this time, but
this is not relevant to this check.
Replace center airbag sensor assembly.
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±75
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OKNG
OKNG
7Check D squib.
C
OK
Hint
P1. Turn ignition switch LOCK.
2. Disconnect battery negative (±) terminal cable, andwait at least 90 seconds.
3. Connect steering wheel pad (squib) connector.
4. Connect negative (±) terminal cable to battery, and wait at least 2 seconds.
1. Turn ignition switch ACC or ON, and wait at least 20
seconds.
Clear malfunction code. Turn ignition switch LOCK
and wait at least 20 seconds.
2. Turn ignition switch ACC or ON, and wait at least 20
seconds.
3. Using SST, connect terminals Tc and E
1 of DLC2.
SST 09843±18020
4. Check diagnostic trouble code.
Diagnostic trouble code 11 is not output.
Codes other than code 11 may be output at this time, but
this is not relevant to this check.
Replace steering wheel pad.
8Check P squib.
C
OK
Hint
P1. Turn ignition switch LOCK.
2. Disconnect battery negative (±) terminal cable, and
wait at least 20 seconds.
3. Connect front passenger airbag assembly (squib) connector.
4. Disconnect steering wheel pad (squib) connector.
5. Connect negative (±) terminal cable to battery and wait at least 2 seconds.
1. Turn ignition switch ACC or ON, and wait at least 20
seconds.
Clear malfunction code. Turn ignition switch LOCK
and wait at least 20 seconds.
2. Turn ignition switch ACC or ON, and wait at least 20
seconds.
3. Using SST, connect terminals Tc and E
1 of DLC2.
4. Check diagnostic trouble code.
Diagnostic trouble code 11 is not output.
Codes other than code 11 nay be output at this time, but
they are not relevant to this check.
Replace front passenger airbag assembly.
RS±76
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
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