1991 LEXUS SC300 ignition

188
SHIFT LOCK
1E
21E 17 1I 10
7 8 SHIFT LOCK
CONTROL SW
SHIFT LOCK
SOLENOID
TIMER
3
2 4
5
1
P1
±P
P2
SLS±
SLS+
1 2
IF 15A
CIG
15A
ECU±IG 15A
STOP
KEY INTERLOCK
SOLENOID
[IGNITION SW] STOP LIGHT
SW
ACC IG STP
KLS+ EL±RL
G±W G
G±R
V
W±B
W±B W±B
L±R
B±R
G±W G±W W B±R
L±R
SHIFT LOCK ECU
FROM POWER SOURCE SYSTEM
(
SEE PAGE 56 )
I15 S12
S10
1H
1
3A
5
3G
6
1E
20
IG1
12
1H
13
1J
1 1E
18
V
3A
1 3H
15
W±B
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189
WHEN THE IGNITION SW IS TURNED TO ACC POSITION THE CURRENT FROM THE CIG FUSE FLOWS TO TERMINAL 1 OF THE SHIFT
LOCK ECU, IN THE ON POSITION, THE CURRENT FROM THE ECU±IG FUSE FLOWS TO TERMINAL 5 OF THE ECU.
1. SHIFT LOCK MECHANISM
WITH THE IGNITION SW ON, WHEN A SIGNAL THAT THE BRAKE PEDAL IS DEPRESSED (STOP LIGHT SW ON) AND A SIGNAL THAT
THE SHIFT LEVER IS PUT IN ªPº RANGE (CONTINUITY BETWEEN P1 AND P OF THE SHIFT LOCK CONTROL SW) IS INPUT TO THE
ECU, THE ECU OPERATES AND CURRENT FLOWS FROM TERMINAL 5 OF THE ECU " TERMINAL SL+ OF THE SHIFT LOCK
SOLENOID " SOLENOID " TERMINAL SL± " TERMINAL 3 OF THE ECU " GROUND. THIS CAUSES THE SHIFT LOCK SOLENOID TO
TURN ON (PLATE STOPPER DISENGAGES) AND THE SHIFT LEVER CAN SHIFT INTO RANGE OTHER THAN THE ªPº RANGE.
2. KEY INTER LOCK MECHANISM
WITH THE IGNITION SW ON OR ACC POSITION, WHEN THE SHIFT LEVER IS PUT IN ªPº RANGE (NO CONTINUIT\
Y BETWEEN P2 AND P
OF SHIFT LOCK CONTROL SW), THE CURRENT FLOWING FROM TERMINAL 2 OF THE ECU " KEY INTER LOCK SOLENOID IS CUT
OFF. THIS CAUSES THE KEY INTER LOCK SOLENOID TO TURN OFF (LOCK LEVER DISENGAGES FROM LOCK POSITION) AND THE
IGNITION KEY CAN BE TURNED FROM ACC TO LOCK POSITION. IF THE IGNITION IS LEFT IN ACC OR ON POSITION WITH THE SHIFT
LEVER IN OTHER THAN ªPº RANGE, THAN AFTER APPROX. ONE HOUR THE ECU\
OPERATES TO RELEASE THE LOCK.
S10 SHIFT LOCK ECU
1±GROUND : APPROX. 12 VOLTS WITH IGNITION SW AT ACC OR ON POSITION
5±GROUND : APPROX. 12 VOLTS WITH IGNITION SW AT ON POSITION
3±GROUND : ALWAYS CONTINUITY
4±GROUND : APPROX. 12 VOLTS WITH BRAKE PEDAL DEPRESSED
S12 STOP LIGHT SW
2±1 : CLOSED WITH BRAKE PEDAL DEPRESSED
: PARTS LOCATION
CODESEE PAGECODESEE PAGECODESEE PAGE
I1529S1029S1229
: JUNCTION BLOCK AND WIRE HARNESS CONNECTOR
CODESEE PAGEJUNCTION BLOCK AND WIRE HARNESS (CONNECTOR LOCATION)
1E20INSTRUMENT PANEL WIRE
1H
1I20COWL WIRE
1J
20COWL WIRE
3A
3G22INSTRUMENT PANEL WIRE
3H
: CONNECTOR JOINING WIRE HARNESS AND WIRE HARNESS
CODESEE PAGEJOINING WIRE HARNESS AND WIRE HARNESS (CONNECTOR LOCATION)
IG136INSTRUMENT PANEL WIRE AND COWL WIRE (R/B NO. 5)
: GROUND POINTS
CODESEE PAGEGROUND POINTS LOCATION
IF36LEFT KICK PANEL
X 78 12345
12
I15 S 10 S 12
BLACK
SYSTEM OUTLINE
SERVICE HINTS
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177
SRS AIRBAG
NOTICE: When inspecting or repairing the SRS AIRBAG, perform the operation in accord\
ance with the
following precautionary instructions and the procedure and precautions in the Repair Manual for the applicable
model year.

Malfunction symptoms of the airbag system are difficult to confirm, so the diagnostic codes become the most
important source of information when troubleshooting.
When troubleshooting the airbag system, always inspect the diagnostic codes before disconnecting the
battery.

Work must be started after 30 seconds or longer from the time the Ignition SW is set to the ªLOCKº position
and the negative (±) terminal cable is disconnected from the battery.
(The airbag system is equipped with a back±up power source so that if work is started within 30 seconds of
disconnecting the negative (±) terminal cable of the battery, the airbag may be deployed.)
When the negative (±) terminal cable is disconnected from the battery, memory of the clock and audio systems
will be cancelled. So before starting work, make a record of the contents memorized by each me\
mory system.
Then when work is finished, reset the clock and audio system as before.
When the vehicle has tilt and telescopic steering, power seat, outside r\
ear view mirror and power shoulder
belt anchorage, which are all equipped with memory function, it is not possible to make a record of the memory
contents. So when the operation is finished, it will be necessary to explain this\
fact to the customer, and
request the customer to adjust the features and reset the memory.
To avoid erasing the memory of each memory system, never use a back±up \
power supply from outside the
vehicle.

When removing the steering wheel pad or handling a new steering wheel pad, keep the pad upper surfa\
ce
facing upward. Also, lock the lock lever of the twin lock type connector\
at the rear of the pad and take care
not to damage the connector.
(Storing the pad with its metallic surface up may lead to a serious accident if \
the airbag inflates for some
reason).

Store the steering wheel pad where the ambient temperature remains below\
93 °C (200 °F), without high
humidity and away from electrical noise.

Never use airbag parts from another vehicle. When replacing airbag parts\
, replace them with new parts.

Never disassemble or repair the steering wheel pad, center airbag sensor asse\
mbly or front airbag sensors.

Before repairing the body, remove the airbag sensors if during repair shocks are likely to be app\
lied to the
sensors due to vibration of the body or direct tapping with tools or oth\
er parts.

Do not reuse a steering wheel pad or front airbag sensors.
After evaluating whether the center airbag sensor assembly is damaged or not, decide whether or not to reuse
it. (See the Repair Manual for the method for evaluating the center airbag\
sensor assembly.)

When troubleshooting the airbag system, use a high±impedance (Min. 1\
0k W/V) tester.

The vehicle wiring harness exclusively for the airbag system is distinguish\
ed by corrugated yellow tubing, as
are the connectors.

Do not measure the resistance of the airbag squib.
(It is possible this will deploy the airbag and is very dangerous.)

If the wire harness used in the airbag system is damaged, replace the wh\
ole wire harness assembly.
When the connector to the airbag front sensors can be repaired alone (when \
there is no damage to the wire
harness), use the repair wire specially designed for the purpose.
(Refer to the Repair Manual for the applicable Model year for details o\
f the replacement method.)

INFORMATION LABELS (NOTICES) are attached to the periphery of the airbag componen\
ts. Follow the
instructions on the notices.
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181
THE SRS (SUPPLEMENTAL RESTRAINT SYSTEM) AIRBAG IS A DRIVER PROTECTION DEVICE WHICH HAS A SUPPLEMENTAL ROLE
TO THE SEAT BELTS.
CURRENT FLOWS CONSTANTLY TO TERMINAL 6 OF THE CENTER AIRBAG SENSOR ASSEMBLY. WHEN THE IGNITION SW IS
TURNED TO ACC OR ON, CURRENT FROM THE CIG FUSE FLOWS TO TERMINAL 14 OF THE CENTER AIRBAG SENSOR ASSEMBLY.
ONLY WHEN THE IGNITION SW IS ON DOES THE CURRENT FROM THE IGN FUSE TO TERMINAL 7 .
IF AN ACCIDENT OCCURS WHILE DRIVING, DECELERATION CAUSED BY A FRONTAL IMPACT IS DETECTED BY EACH SENSOR AND
SWITCH, AND WHEN THE FRONTAL IMPACT EXCEEDS A SET LEVEL (WHEN THE SAFING SENSOR BUILT INTO THE CENTER AIRBAG
SENSOR ASSEMBLY IS ON AND THE CENTER AIRBAG SENSOR IS ON, FRONT AIRBAG SENSORS ARE OFF), CURRENT \
FROM THE
CIG OR IGN FUSE FLOWS TO TERMINAL 11 OF THE CENTER AIRBAG SENSOR ASSEMBLY " TERMINAL 1 OF THE AIRBAG SQUIB "
SQUIB " TERMINAL 2 " TERMINAL 10 OF CENTER AIRBAG SENSOR ASSEMBLY " TERMINAL 8, TERMINAL 13 OR BODY GROUND
" GROUND.
WHEN THE SAFING SENSOR BUILT INTO THE CENTER AIRBAG SENSOR ASSEMBLY IS ON AND THE FRONT AIRBAG SENSOR LH OR
RH IS ON, CENTER AIRBAG SENSOR IS OFF AND CURRENT FROM THE CIG OR IGN FUSE FLOWS TO TERMINAL 11 OF THE CENTER
AIRBAG SENSOR ASSEMBLY " TERMINAL 1 OF THE AIRBAG SQUIB " SQUIB " TERMINAL 2 " TERMINAL 10 OF CENTER AIRBAG
SENSOR ASSEMBLY " TERMINAL 3 OR 4 " TERMINAL 1 OF FRONT AIRBAG SENSOR " TERMINAL 2 " TERMINAL 2 OR 5 OF
CENTER AIRBAG SENSOR ASSEMBLY " TERMINAL 8, TERMINAL 13 OR BODY GROUND " GROUND , WHEN THE SAFING SENSOR
BUILT INTO THE CENTER AIRBAG SENSOR ASSEMBLY IS ON, AND THE FRONT AIRBAG SENSOR LH OR RH IS ON AND CENTER
AIRBAG SENSOR IS ON ONE OF THE ABOVE±MENTIONED CIRCUITS IS ACTIVATED SO THAT CURRENT FLOWS TO THE AIRBAG
SQUIB AND CAUSES IT TO OPERATE. THE BAG STORED INSIDE THE STEERING WHEEL PAD IS INSTANTANEOUSLY EXPANDED TO
SOFTEN THE SHOCK TO THE DRIVER.
: PARTS LOCATION
CODESEE PAGECODESEE PAGECODESEE PAGE
A2928C1228T 629
C 326F 126
C1028F 226
: JUNCTION BLOCK AND WIRE HARNESS CONNECTOR
CODESEE PAGEJUNCTION BLOCK AND WIRE HARNESS (CONNECTOR LOCATION)
1E20INSTRUMENT PANEL WIRE
1G20COWL NO. 2 WIRE
1J20COWL WIRE
3A
3B
3D22INSTRUMENT PANEL WIRE
3E
3H
: CONNECTOR JOINING WIRE HARNESS AND WIRE HARNESS
CODESEE PAGEJOINING WIRE HARNESS AND WIRE HARNESS (CONNECTOR LOCATION)
IK136ENGINE WIRE AND INSTRUMENT PANEL WIRE (RIGHT KICK PANEL)
: GROUND POINTS
CODESEE PAGEGROUND POINTS LOCATION
EC34FRONT SIDE OF INTAKE MANIFOLD
ED34REAR SIDE OF CYLINDER HEAD RH
IF36LEFT KICK PANEL
: SPLICE POINTS
CODESEE PAGEWIRE HARNESS WITH SPLICE POINTSCODESEE PAGEWIRE HARNESS WITH SPLICE POINTS
E2034ENGINE WIRE
SYSTEM OUTLINE
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62
STARTING AND IGNITION
AM1
AM2
11 4
1
6
ST1
IG2
A
1
B 1 1J
6
1J
7
2
22
1B
4 1K
4
6 9 4 14 13 7 M
IE1
16
EB2
1 IE1
15
E19
L±O
L±O B
B
B WW±R
W± RW
W±L
W±RW±L W
W
B±O
B±W
B
B
B
B
W± R
BATTERY
STARTER
31
52
IGNITION SW
40A
IGSW
STARTER
RELAY 7. 5A
ST
FUSE BLOCK
TO THEFT DETERRENT AND
DOOR LOCK ECU 30A AM2
120A ALT
100A AM1
30A INJ
60A MAIN
I15
S6 , S7
F9
BA
3
4
2 1
2
3 IJ1
6
EB1
3
IJ28
IJ1
7
B±O
B
B
B
BB±W B±W
B±W
(A/T )
( M/T )
NEUTRAL
START SW CLUTCH
START SW
N1 C23
( A/T )
( M/T )
2
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63
E18E14
E20
2 1
ED
W± L
B
B±O
B
W± B B±OB±O
B±O
BB
B± O
TO COMBINATION
METER
(
TACHO )12
DISTRIBTOR
IGNITION COIL
I4
D13
IG± TAC +B
IGF IGT C±
IGNITER
CHECK
CONNECTOR
C3 I2
435
19
12
STA IGF IGT
77 58 57
ENGINE AND ECT ECU (
A/T )
E10
NOISE FILTER
(
FOR IGNITION SYSTEM )
N31234
27 26 25 7 NE G1 G2 G± NE G1 G2 G±
L
R Y
B
W±Y
R±Y
ENGINE ECU
(
M/T )
E12
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64
STARTING AND IGNITION
C 4 COLD START INJECTOR
2±1 : APPROX. 12 VOLTS WHILE START INJECTOR TIME SW IS CLOSED AND STARTER CRANKING
I15 IGNITION SW
4±1 : CLOSED WITH IGNITION SW AT ST POSITION
11±6: CLOSED WITH IGNITION SW AT ON OR ST POSITION
N 1 NEUTRAL START SW
3±2 : CLOSED WITH A/T SHIFT LEVER IN P OR N POSITION
S 6(B), S 7(A) STARTER
POINTS CLOSED WITH NEUTRAL START SW ON AND IGNITION SW AT ST POSITION
: PARTS LOCATION
CODESEE PAGECODESEE PAGECODESEE PAGE
C 326F 926N 327
C2328I 227S 6B27
D1326I 427S 7A27
E1028I1529
E1228N 127
: RELAY BLOCKS
CODESEE PAGERELAY BLOCKS (RELAY BLOCK LOCATION)
219ENGINE COMPARTMENT LEFT
: JUNCTION BLOCK AND WIRE HARNESS CONNECTOR
CODESEE PAGEJUNCTION BLOCK AND WIRE HARNESS (CONNECTOR LOCATION)
1B20ENGINE ROOM MAIN WIRE
1J20COWL WIRE1K20COWL WIRE
: CONNECTOR JOINING WIRE HARNESS AND WIRE HARNESS
CODESEE PAGEJOINING WIRE HARNESS AND WIRE HARNESS (CONNECTOR LOCATION)
EB134ENGINE WIRE AND ENGINE ROOM MAIN WIRE (FRONT SIDE OF R/B NO 2)EB234ENGINE WIRE AND ENGINE ROOM MAIN WIRE (FRONT SIDE OF R/B NO. 2)
IE136ENGINE ROOM MAIN WIRE AND COWL WIRE (R/B NO. 4)
IJ136ENGINE WIRE AND COWL WIRE (RIGHT KICK PANEL)
IJ236ENGINE WIRE AND COWL WIRE (RIGHT KICK PANEL)
: GROUND POINTS
CODESEE PAGEGROUND POINTS LOCATION
ED34REAR SIDE OF INTAKE MANIFOLD
: SPLICE POINTS
CODESEE PAGEWIRE HARNESS WITH SPLICE POINTSCODESEE PAGEWIRE HARNESS WITH SPLICE POINTS
E1434ENGINE WIREE1934ENGINE WIREE1834ENGINE WIREE2034ENGINE WIRE
SERVICE HINTS
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99
CURRENT IS APPLIED AT ALL TIMES THROUGH A STOP FUSE TO TERMINAL 2 OF THE STOP LIGHT SW.
WHEN THE IGNITION SW IS TURNED ON, CURRENT FLOWS FROM THE GAUGE FUSE TO TERMINAL 8 OF THE LIGHT FAILURE
SENSOR, AND ALSO FLOWS THROUGH THE REAR LIGHT WARNING LIGHT TO TERMINAL 4 OF THE LIGHT FAILURE SENSOR.
STOP LIGHT DISCONNECTION WARNING
WHEN THE IGNITION SW IS TURNED ON AND THE BRAKE PEDAL IS PRESSED (STOP LIGHT SW ON), IF THE STOP LIGHT CIRCUIT IS
OPEN, THE CURRENT FLOWING FROM TERMINAL 7 OF THE LIGHT FAILURE SENSOR TO TERMINALS 1, 2 CHANGES, SO THE LIGHT
FAILURE SENSOR DETECTS THE DISCONNECTION AND THE WARNING CIRCUIT OF THE LIGHT FAILURE SENSOR IS ACTIVATED.
AS A RESULT, THE CURRENT FLOWS FROM TERMINAL 4 OF THE LIGHT FAILURE SENSOR " TERMINAL 11 " GROUND AND TURNS
THE REAR LIGHT WARNING LIGHT ON. BY PRESSING THE BRAKE PEDAL, THE CURRENT FLOWING TO TERMINAL 8 OF THE LIGHT
FAILURE SENSOR KEEPS THE WARNING CIRCUIT ON HOLD AND THE WARNING LIGHT ON UNTIL THE IGNITION SW IS TURNED OFF.
S12 STOP LIGHT SW
2±1: CLOSED WITH BRAKE PEDAL DEPRESSED
L 3 LIGHT FAILURE SENSOR
1, 2, 7±GROUND : APPROX. 12 VOLTS WITH STOP LIGHT SW ON
4, 8±GROUND : APPROX. 12 VOLTS WITH IGNITION SW AT ON POSITION
11±GROUND : ALWAYS CONTINUITY
: PARTS LOCATION
CODESEE PAGECODESEE PAGECODESEE PAGE
C13B28H 930R1131
C14A28L 330S1229
H 830R1031
: JUNCTION BLOCK AND WIRE HARNESS CONNECTOR
CODESEE PAGEJUNCTION BLOCK AND WIRE HARNESS (CONNECTOR LOCATION)
1C20FLOOR WIRE
1E20INSTRUMENT PANEL WIRE
1H20COWL WIRE1I20COWL WIRE
3A22INSTRUMENT PANEL WIRE3D22INSTRUMENT PANEL WIRE
: CONNECTOR JOINING WIRE HARNESS AND WIRE HARNESS
CODESEE PAGEJOINING WIRE HARNESS AND WIRE HARNESS (CONNECTOR LOCATION)
BU140FLOOR WIRE AND INSTRUMENT PANEL WIRE (LEFT KICK PANEL)
Bc140FLOOR NO. 3 WIRE AND FLOOR WIRE (UNDER THE LEFT SIDE OF REAR SEAT CUSHION)
Bd140FLOOR NO. 3 WIRE AND LUGGAGE NO. 2 WIRE (RIGHT SIDE OF LUGGAGE COMPARTMENT)
: GROUND POINTS
CODESEE PAGEGROUND POINTS LOCATION
BL40UNDER THE CENTER PILLAR RH
BM40BACK PANEL CENTER
: SPLICE POINTS
CODESEE PAGEWIRE HARNESS WITH SPLICE POINTSCODESEE PAGEWIRE HARNESS WITH SPLICE POINTS
B1040FLOOR MAIN WIREB1540FLOOR MAIN WIRE
B1440FLOOR MAIN WIREB2140FLOOR NO. 3 WIRE
SYSTEM OUTLINE
SERVICE HINTS
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