1991 LEXUS SC400 airbag off

FRONT AIRBAG SENSOR
INSPECTION ITEMS
RS015±0C
1. VEHICLES NOT INVOLVED IN A COLLISIONPerform a diagnostic system check.
(See page RS±59)
2. VEHICLES INVOLVED IN A COLLISION
(a) Perform a diagnostic system check. (See page RS±59)
(b) If the front fender of the car or its periphery is damaged, perform visual check for damage to the front airbag sensor,
which includes the following items even if the airbag was not
deployed:
wBracket deformation.
w Peeling of paint from the bracket.
w Cracks, dents or chips in the case.
w Cracks and dents in, or chipping and scratches of the
connector.
w Peeling off of the label or damage to the series number.
Also refer to the body dimension drawings in the BODY sec-
tion and check the dimensions and mounting surface angle
of the body area where the front airbag sensors are mounted.
(The SRS may malfunction, or may not work, if the mounting
angle or dimensions of the sensor mount are not correct.)
REPLACEMENT REQUIREMENTS
RS016±06
In the following cases, replace the front airbag sensor.
NOTICE: for replacement of the front airbag sensor, see
page RS±42 , ªFRONT AIRBAG SENSOR REMOVAL AND
INSTALLATIONº and be sure to follow the correct proce-
dure.
w If the SRS has been deployed in a collision.
(Replace both the left and right airbag sensors.)
w If the front airbag sensor has been found to be faulty in
troubleshooting.
w If the front airbag sensor has been found to be faulty
during the check in item 2±(b).
w If the front airbag sensor has been dropped.
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SUPPLEMENTAL RESTRAINT SYSTEM FRONT AIRBAG SENSORRS±41
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HOW TO PROCEED WITH TROUBLESHOOTING
Malfunction symptoms of the supplemental restraint system are difficult to confirm, so the diagnostic
trouble codes become the most important source of information when troubleshoot\
ing. Perform trouble-
shooting of the supplemental restraint system in accordance with the fol\
lowing procedure:
HINT: Do not disconnect the battery negative (±) terminal cable until st\
ep , Diagnostic Trouble Code
Check and Recording, has been completed.

CUSTOMER PROBLEM ANALYSIS
Using the CUSTOMER PROBLEM ANALYSIS CHECK SHEET (See page RS±58) for reference, ask the
customer in as much detail as possible about the problem.
WARNING LIGHT CHECK
Check the SRS warning light. If the light remains on, a malfunction is stored in the center airbag sensor,
assembly, so proceed to step . If the SRS warning light is not on, a malfunction has occurred in the SRS
warning light circuit, so perform troubleshooting for 22.
HINT: 22 is recorded when a malfunction occurs in the SRS warning light syst\
em.
If an open malfunction occurs in the SRS warning light system, the SRS w\
arning light does not light up,
so that until the malfunction is repaired, the diagnostic trouble codes (\
including 22) cannot be confirmed.
 DIAGNOSTIC TROUBLE CODE CHECK AND RECORDING
Check the di agnostic trouble codes and make a note of any malfunction codes which ar\
e output. If a normal
code is output, an abnormality in the power source circuit may have occurred\
, so perform troubleshooting
for source voltage in step .
If 22 is output, skip steps  and  and proceed to step .
 MALFUNCTION CODE CLEARANCE
Clear the malfunction code.
HINT: The malfunction code output in step  indicates that a malfunction has occurred in the circuit desig-
nated by the malfunction code, but does not indicate whether the malfunction \
is still occurring or whether
it was in the past.
Accordingly, it is necessary to find out the present condition of the malfunction oc\
currence by clearing the
malfunction code and performing the diagnostic code check again. If this\
operation is neglected and trou-
bleshooting is performed using only the malfunction code confirmed in step , isolating the problem com-
ponent becomes difficult and invites mistaken diagnosis.
 DIAGNOSTIC TROUBLE CODE CHECK AND RECORDING  SYMPTOM SIMULATION
After repeating ignition switch ON±OFF operation (ON: wait 20 secs, OFF: \
wait 20 secs.) 5 times, check
the diagnostic trouble codes. If any code is output, the malfunction is sti\
ll occurring, so proceed to step .
Bearing in mind that a malfunction code was registered in step , provided that the normal code is present-
ly output, use the methods described in step  to simulate the malfunction.
RS±54
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SYMPTOM SIMULATION
ªIntermittent troubles or problemsº are the malfunctions about which the customer \
has a complaint, but which
do not occur and can not be confirmed in the workshop. The intermittent pr\
oblems also include complaints about
the SRS warning light going on and off erratically.
The self±diagnostic system stores the circuit of the intermittent pro\
blem in memory even if the ignition switch
is turned off.
And, for accurate diagnosis of the problems, ask the customer to obtain info\
rmation as much as possible follow-
ing the customer problem analysis check sheet (See page RS±58) and try to reproduce the intermittent problem.
The problem simulation methods described below are the effective ways for this nature of problem to produce
the problem conditions by applying vibration, heat, and humidity.
1VIBRATION METHOD: When vibration seems to be the major cause.
CONNECTORS
Slightly shake the connector vertically and horizontally.
(Inspection of connectors)
(a) Does the wire harness connecting with its corre-
sponding part have insufficient slack?
(b) Are the terminals dirty?
(c) Are the terminals making loose contact due to termi-
nals spread?
WIRE HARNESS
Slightly shake the wire harness vertically and horizontal-
ly. The connector joint, fulcrum of the vibration, and
body through portion are the major areas to be checked
thoroughly.
PARTS AND SENSORS
Apply vibration slightly by a finger to the part or sensor
considered to be the problem cause and check if the
malfunction will occur.
Caution: Do not apply vibration to the center
airbag sensor assembly.
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SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±65
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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±
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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)
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SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±69
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DTC22SRS Warning Light System Malfunction
CIRCUIT DESCRIPTION
The SRS warning light is located on the combination meter.
When the supplemental restraint system is normal, the SRS warning light ligh\
ts up for approx. 6 seconds after
the ignition switch is turned from LOCK position to ACC or ON position, and then turn\
s off automatically. If there
is a malfunction in the supplemental restraint system, the SRS warning l\
ight lights up to inform the driver of the
abnormality.
When terminals Tc and E
1 of the DLC2 are connected, the diagnostic trouble code is displayed by the blinking
of the SRS warning light.
The SRS warning light circuit is equipped with an electrical connection che\
ck mechanism which detects when
the connector to the center airbag sensor assembly is not properly connecte\
d.
If the connector to the center airbag sensor assembly is not properly conn\
ected, the SRS warning light will not
light up.
Diagnostic trouble code 22 is recorded when a malfunction occurs in the SRS warnin\
g light system. If an OPEN
malfunction occurs in the SRS warning light system, the SRS warning light does not light up, so that until the
malfunction is repaired, the diagnostic trouble codes (including 22) c\
annot be confirmed.
DTC No.Trouble Area
22 Open circuit in SRS warning light system.
 Center airbag sensor assembly malfunction.
RS±102±
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567 8
21 LEXUS SC300(
Cont ' d )
AIR BAG
CHA RGE
OIL
OIL LEVEL COOLANT
LEVEL REAR
LI GHT
PWR
ABS TRAC
TRAC OFF
CRUISE WASHER
O/ D OFF
FUEL
SEAT BELTP
R N D 2 L
A
C
C A
A
B
B
B
C
C
C
C
C
C
C
B C
C
B
B
BA
B
A
A
C
CA A A A A A A A
C
C
C
C C C A C C B B B B
B A A C C
10 : 00
BK 1E
18 3D
10
3A
1
1J
1 1K
12
IH IF ED
IK1
8
IK2 IK1
9
1
E
3
E
2
E
1
D
BU110
BU1
3
BU1
4 11
11
1
14
19
8
18
11
13 6
18
17
16
20
19
15
13
3
15 5
1
20 9
18 8
11
87 1 2 3 4 5 16 17
2
3
4
5 10 9
12 23 12 4 17 16 7
6
15
10 22 21
W± R
RY
B±O
Y±B
V± R
V±Y
R±W
L±R
W
R± Y B
V±W V
R
L±R
P±L
Y±B
B±Y
B± W
W±B BR
B
W± B W± B BR±B
Y± G
B
Y±G
BR±B
W± B
W±B
W±B
BR±B W± B BR
Y±G
WATER
TEMP.HI GH BEAM TURN
LH
RH
BRAKE DOOR
TACHO
TRI P
SPEED
ILLUMINATIONCHECK±
ENGINE
FUEL
See Taillight and
St op Light Sy stem
<4±6><5±6>
SeeEngineControlSystem
<2±3>
Se e ABS Sy st e m< 8± 7> < 9± 3>
See Cruise Control System
< 16±3>Se e ABS an d Tr act io n
Control System< 8±7>
SeeECTandA/TIndicator
System< 3±5>
D
F1 7 , F18 E
FUEL SENDER Y±B
B±Y
B±W 24
See SRS Airbag System< 15±4>
See Charging Sy stem< 1±2>
See Headlight Sys tem< 4±1> < 5±1>
See Turn Signal and
Hazard Warning
Light Sy stem< 7±3>
See ECT System< 3±5>
From Neutr al St art SW< 1±3>
See Interier Light System< 6±3> From Igniter º TACº < 1±5>
To Engine and ECT ECU< 2±7>
To Cruise Control ECU< 16±3>
To PPS ECU< 15±2> See Illumination System
<4±7><5±7>
See ECT and A/T Indic ator
Syst em< 3±6>
See Unlock and Seat Belt
Warning Syst em< 4±4> < 5±4>
W3
WATER TEMP.
SENDER
Combination Meter
1
COMBINATION METER C12 , C13 , C14
A
AB IG1
8
Under the
c ent er
pillar LH Under the
as htr ay LH
Lef t
kick panelRear side of
c ylinder head RH
C
2
G 2
F
1
F 14
L±R
P
P
SH OR T C ON NE CT OR
S2 2 G , S23 F L±R
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244
Rear Window Defogger
and Mirror Heater
Remote Control Mirror
Seat Heater
Shift Lock
SRS AIRBAG
Starting
Taillight and
Stop Light
Theft Deterrent and
Door Lock Control
Turn Signal and Hazard
Warning Light
Wiper and Washer
Wireless Door Lock
Remote Control
Horn
Ignition
Illumination
Interior Light
Liquid Crystal Inner
Rear View Mirror
Moon Roof
Power Seat
(Driver's)
Power Source
Power Window
PPS (Progressive
Power Steering
Radio and Player
ABS and
Traction Control
Automatic
Air Conditioner
Auto Antenna
Back±Up Light
Cellular Mobile
Telephone
Charging
Cigarette Lighter
Combination Meter
Cruise Control
Headlight and Light Auto
Turn Off (for USA)
Headlight
(for Canada) ECT and
A/T Indicator
4±2 16±2 7±2
3±2 21±2 3±8
14±4
18±2 19±4 (w/o CD Player)
20±8 (w/ CD Player)9±2 8±2
4±7 (for USA)
5±7 (for Canada)11±2
12±311±5 (w/ Driving
Position Memory)11±7 12±1 1±5 13±2
6±2 15±2 14±2
13±2
17±7 7±3 17±2 15±3
1±315±2
Power Tilt and
Power Telescopic12±2
Power Seat (Passengerºs
and Electric Tension Header
5±2 2±2
Cornering Light ABS (Anti±Lock
Brake System)
22±2
Engine Control Unlock and Seat
Belt Warning
1±2
23±2 (w/o Driving
Position Memory)
1 23±119±2 (w/o CD Player
20±2 (w/ CD Player
14±310±2 (w/ Memory)
5±7 (w/o Memory)
4±3 (for USA)
5±3 (for Canada) 4±5 (for USA)
5±5 (for Canada)
OVERALL ELECTRICAL WIRING DIAGRAM
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