1991 LEXUS SC400 oxygen sensor

66
.
ENGINE CONTROL
THIS SYSTEM UTILIZES AN ECU AND MAINTAINS OVERALL CONTROL OF THE ENGINE, TRANSMISSION AND SO ON. AN OUTLINE O\
F
THE ENGINE CONTROL IS EXPLAINED HERE.
1. INPUT SIGNALS
(1) WATER TEMP. SIGNAL CIRCUITTHE WATER TEMP. SENSOR DETECTS THE ENGINE COOLANT TEMP. AND HAS A BUILT±IN THERMISTOR WITH A RESISTANCE
WHICH VARIES ACCORDING TO THE WATER TEMP. THE WATER TEMP. IS INPUT INTO TERMINAL THW OF ENGINE CONTROL
ECU AS A CONTROL SIGNAL.
(2) INTAKE AIR TEMP. SIGNAL CIRCUIT THE INTAKE AIR TEMP. SENSOR IS INSTALLED IN THE AIR FLOW METER AND DETECTS THE INTAKE AIR TEMP., WHICH IS INPUT
AS A CONTROL SIGNAL TO TERMINAL THA OF ENGINE CONTROL ECU.
(3) OXYGEN SENSOR SIGNAL CIRCUIT THE OXYGEN DENSITY IN THE EXHAUST EMISSION IS DETECTED AND INPUT AS A CONTR\
OL SIGNAL FROM THE OXYGEN
SENSOR NO. 1 AND NO. 2 TO TERMINALS OX1, OX2 OF THE ECU AND FROM THE OXYGEN SENSOR SUB (FOR CALIFORNIA) TO
TERMINAL OX3 OF THE ECU.
TO STABILIZE DETECTION PERFORMANCE BY THE OXYGEN SENSOR SUB (FOR CALIFORNIA)\
IS WARMED. THIS HEATER IS
ALSO CONTROLLED BY THE ECU (HT).
(4) RPM SIGNAL CIRCUIT CRANKSHAFT POSITION IS DETECTED BY THE PICK±UP COIL INSTALLED INSIDE THE DISTRIBUTOR. CRANKSHAFT POSITION
IS INPUT AS A CONTROL SIGNAL TO TERMINALS G1 AND G2 OF THE ECU, AND RPM IS INPUT TO TERMINAL NE.
(5) THROTTLE SIGNAL CIRCUIT THE THROTTLE POSITION SENSOR DETECTS THE THROTTLE VALVE OPENING ANGLE AS A CONTROL SIGNAL, WHICH IS
INPUT INTO TERMINAL VTA1 OF THE ECU. WHEN THE VALVE IS COMPLETELY CLOSED, THE CONTROL SIGNAL IS INPUT INTO
TERMINAL IDL1 .
(6) VEHICLE SPEED CIRCUIT THE VEHICLE SPEED IS DETECTED BY SPEED SENSOR NO. 1 INSTALLED IN THE TRANSMISSION AND THE SIGNAL IS INPUT TO
TERMINAL SPD OF THE ECU VIA THE COMB. METER.
(7) NEUTRAL START SIGNAL CIRCUIT THE NEUTRAL START SW DETECTS WHETHER THE SHIFT POSITION IS IN NEUTRAL OR NOT, AND THE SIGNAL IS INPUT INTO
TERMINAL NSW OF THE ECU.
(8) AIRCONDITIONING SW SIGNAL CIRCUIT THE OPERATING VOLTAGE OF THE A/C MAGNETIC CLUTCH IS DETECTED AND THE SIGNAL IS INPUT INTO TERMINAL ACMG OF
ECU AS A CONTROL SIGNAL.
(9) BATTERY SIGNAL CIRCUIT VOLTAGE IS CONSTANTLY APPLIED TO TERMINAL BATT OF THE ECU. WITH THE IGNITION SW TURNED ON, THE VOLTAGE FOR
ECU START±UP POWER SUPPLY IS APPLIED TO TERMINALS +B AND +B1 OF ECU VIA EFI MAIN RELAY.
THE CURRENT FLOWING THROUGH THE IGN FUSE FLOWS TO TERMINAL IGSW OF THE ECU.
(10) INTAKE AIR VOLUME SIGNAL CIRCUIT INTAKE AIR VOLUME IS DETECTED BY THE AIR FLOW METER AND THE SIGNAL IS INPUT TO TERMINAL KS OF THE ECU AS A
CONTROL SIGNAL.
(11) STOP LIGHT SW SIGNAL CIRCUIT THE STOP LIGHT SW IS USED TO DETECT WHETHER OR NOT THE VEHICLE IS BRAKING AND THE SIGNAL IS INPUT INTO
TERMINAL STP OF THE ECU AS A CONTROL SIGNAL.
(12) STA SIGNAL CIRCUIT TO CONFIRM WHETHER THE ENGINE IS CRANKING, THE VOLTAGE APPLIED TO THE STARTER MOTOR DURING CRANKING IS
DETECTED AND THE SIGNAL IS INPUT INTO TERMINAL STA OF THE ECU AS A CONTROL SIGNAL.
(13) ENGINE KNOCK SIGNAL CIRCUIT ENGINE KNOCKING IS DETECTED BY KNOCK SENSOR NO. 1 AND NO. 2 AND THE SIGN\
AL IS INPUT INTO TERMINALS KNK1 AND
KNK2 AS A CONTROL SIGNAL.
SYSTEM OUTLINE
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67
2. CONTROL SYSTEM
*EFI (ELECTRONIC FUEL INJECTION) SYSTEM
THE EFI SYSTEM MONITORS THE ENGINE CONDITION THROUGH THE SIGNALS INPUT FROM EACH SENSOR (IN\
PUT SIGNALS
FROM (1) TO (13) ETC.) TO THE ECU. THE BEST FUEL INJECTION TIMING IS DECIDED BASED ON THIS DATA AND THE PROGRAM
MEMORIZED BY THE ECU, AND THE CONTROL SIGNAL IS OUTPUT TO TERMINALS #10, #20, #30, #40, #50 AND #60 OF THE ECU TO
OPERATE THE INJECTOR. (INJECT THE FUEL). THE EFI SYSTEM PRODUCES CONTROL OF FUEL INJECTION OPERATION BY THE
ECU IN RESPONSE TO THE DRIVING CONDITIONS.
* ESA (ELECTRONIC SPARK ADVANCE) SYSTEM
THE ESA SYSTEM MONITORS THE ENGINE CONDITION THROUGH THE SIGNALS INPUT TO THE ECU FROM EACH SENSOR (INPUT
SIGNALS FROM (1), (2), (4) TO (13) ETC.). THE BEST IGNITION TIMING IS DECIDED ACCORDING TO THIS DATA AND THE
MEMORIZED DATA IN THE ECU AND THE CONTROL SIGNAL IS OUTPUT TO TERMINAL IGT THIS SIGNAL CONTROLS THE IGNITER
TO PROVIDE THE BEST IGNITION TIMING FOR THE DRIVING CONDITIONS.
* OXYGEN SENSOR HEATER CONTROL SYSTEM (USA SPEC.)
THE OXYGEN SENSOR HEATER CONTROL SYSTEM TURNS THE HEATER ON WHEN THE INTAKE AIR VOLUME IS LOW (TEMP. OF
EXHAUST EMISSIONS IS LOW), AND WARMS UP THE OXYGEN SENSOR TO IMPROVE DETECTION PERFORMANCE OF THE
SENSOR.
THE ECU EVALUATES THE SIGNALS FROM EACH SENSOR (INPUT SIGNALS FROM (1), (2), (4)\
, (9) TO (11) ETC.,) AND OUTPUTS
CURRENT TO TERMINAL HT TO CONTROL THE HEATER.
* ISC (IDLE SPEED CONTROL) SYSTEM
THE ISC SYSTEM (STEP MOTOR TYPE) INCREASES THE RPM AND PROVIDES IDLING STABILITY FOR FAST IDLE±UP WHEN THE
ENGINE IS COLD, AND WHEN THE IDLE SPEED HAS DROPPED DUE TO ELECTRICAL LOAD AND SO ON. THE ECU EVALUATES
THE SIGNALS FROM EACH SENSOR (INPUT SIGNALS FROM (1), (4), (5), (8)\
, (9), (11) ETC.), OUTPUTS CURRENT TO TERMINAL ISC1,
ISC2, ISC3 AND ISC4 TO CONTROL ISC VALVE.
* EGR CONTROL SYSTEM
THE EGR CONTROL SYSTEM DETECTS THE SIGNAL FROM EACH SENSOR (INPUT SIGNALS \
FROM (1), (4), (9), (10) ETC.), AND
OUTPUTS CURRENT TO TERMINAL EGR TO CONTROL THE EGR VALVE.
* FUEL PUMP CONTROL SYSTEM
THE COMPUTER OUTPUTS CURRENT TO TERMINAL FPC AND CONTROLS THE FUEL PUMP ECU AND FUEL PUMP DRIVE SPEED
IN RESPONSE TO CONDITIONS.
* ACIS (ACOUSTIC CONTROL INDUCTION SYSTEM)
ACIS INCLUDES A VALVE IN THE BULKHEAD SEPARATING THE SURGE TANK INTO TWO PARTS. THIS VALE IS OPENED AND
CLOSED IN ACCORDANCE WITH THE DRIVING CONDITIONS TO CONTROL THE INTAKE MANIFOLD LENGTH IN TWO STAGES FOR
INCREASED ENGINE OUTPUT IN ALL RANGES FROM LOW TO HIGH SPEEDS.
THE ECU JUDGES THE VEHICLE SPEED BY THE SIGNALS ((4), (5)) FROM EACH \
SENSOR AND OUTPUTS SIGNALS TO THE
TERMINAL ACIS TO CONTROL THE VSV (FOR OPENING AND CLOSING THE INTAKE CONTROL VALVE).
3. DIAGNOSIS SYSTEM
WITH THE DIAGNOSIS SYSTEM, WHEN THERE IS A MALFUNCTION IN THE ECU SIGNAL\
SYSTEM, THE MALFUNCTIONING SYSTEM IS
RECORDED IN THE MEMORY. THE MALFUNCTIONING SYSTEM CAN BE FOUND BY READING THE CODE DISPLAYED BY THE
CHECKING ENGINE WARNING LIGHT.
4. FAIL±SAFE SYSTEM
WHEN A MALFUNCTION HAS OCCURRED IN ANY SYSTEM, IF THERE IS A POSSIBILITY OF \
ENGINE TROUBLE BEING CAUSED BY
CONTINUED CONTROL BASED ON THE SIGNALS FROM THAT SYSTEM, THE FAIL±SAFE SYSTEM EITHER CONTROLS THE SYSTEM
BY USING DATA (STANDARD VALUES) RECORDED IN THE ECU MEMORY OR ELSE STOPS THE ENGINE.
NOTE: THE SPECIFICATION DESCRIPTIONS ªUSA SPEC.º AND ªEXC. USA SPEC.º USED IN THIS SECTION INDICATE THE
FOLLOWING SPECIFICATIONS.
USA SPEC. : USA (50 STATES) SPECIFICATIONS
EXC. USA SPEC. : USA (EXCEPT CALIFORNIA) AND CANADIAN SPECIFICATIONS.
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ENGINE CONTROL
VC
VTA
IDL
E2
2
134
12 34
E20 E18 E18
B
42
VTA2 B
63
IDL2 B
65
E2 B
64
IDL1 B
43
VTA1 B
41
VC B
45
THA B
66
KS
A
35 PS
B
47 OX2 5
THA KS VC
E2
BR BR
B±R
B±R
WGB
L±Y
B±R
BR
BR
BR
BR
BR R
Y
L±R
BR
Y±B
Y±G L±R
BR
R
Y
L±R BR
R±B
Y±L
E
THROTTLE
POSITION
SENSOR AIR FLOW METER
ENGINE ECU (
M/T )
TO S UB THROTTL E
POSITION SENSOR
(
W/ TRACTI ON
CONTROL )
E11 , E1 2
AB
T2
A9
ENGINE AND ECT ECU (
A/T )
E9 ,E10
A
B
(
FOR USA SPEC. )
1 2 I34
I40I17
I23 I32 B17
E16 I13
I34
I32
IK1 1
BY16
BY1
5
IG33
IK 2
22 IK2 12 BY1 2
BY1
1
1
1 B
48 OX1
B
71 HT
B
61 OX3
EC
BT1
17
LG±B
W
BR
W
BR±W
BR±W W
BR±W
W
R±L
R±L R±L
B±R
BR
B±R
( SHIELDED )
(
SHIELDED )
(
SHIELDED )
W
BR±W
R±B
BR BR BR R±L
G B
L±Y
B±R
BR
BR
BR
BR
(SHIELDED )
G
B
L±Y
B±R BR BR B±R
BR
R±L
BR±W
BR
OXYGEN SENSOR SUB
(FOR USA SPEC. )
O8
42 13
(
*2 )
(
*1 )
(
*2 )(
*1 )
(
*3 )
O3
OXYGEN SENSOR
MAIN NO. 1
(
ON FRONT SIDE )
POWER STERRING
PRESSURE SW P20
O4
OXYGEN SENNSOR
MAIN NO. 2
( ON REAR SIDE )
(
SHIELDED )
(
*3 )
R±L
B±R
B±R
BR
BR (*2 )
( *1 )
BR
( SHIELDED )
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I 1 ISC VALVE
4, 6±5 : APPROX. 21.3
1, 3±2 : APPROX. 21.3
I 6, I 7, I 8, I 9, I10, I11 INJECTOR
1 ± 2 : APPROX. 13.8
O 8 OXYGEN SENSOR SUB (FOR USA SPEC.)
1 ± 2 : APPROX. 5.6(20 °C, 68°F)
T 2 THROTTLE POSITION SENSOR
1 ± 4 : APPROX. 3±7K
1 ± 3 : 2.4±10.7 K WITH THROTTLE VALVE FULLY OPENED POSITION
0.3±5.9 K WITH CLEARANCE BETWEEN LEVER AND STOP SCREW 0MM (0 IN.)
1 ± 2 : LESS THAN 0.5K WITH CLEARANCE BETWEEN LEVER AND STOP SCREW 0.4 MM (0.0157 IN.)
INFINITY WITH CLEARANCE BETWEEN LEVER AND STOP SCREW 0.85MM (0.0335 IN.)
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236
GROUND POINT
FRONT TURN SIGNAL
LIGHT LH
ENGINE HOOD
COURTESY SW
TRACTION PUMP AND
MOTOR
HEATER RELAY
ABS ACTUATOR RELAY
TELEPHONE
TRANSCEIVER
AND SPEAKER RELAY
ENGINE OIL LEVEL
WARNING SW
COMBINATION METER
(E1 )
EFI ECU
TRACTION ECU
CHECK CONNECTOR
(
E1 ) CORNERING LIGHT LH
FRONT SIDE MAKER
LIGHT LH
BRAKE FLUID LEVEL
SW
FRONT CLEARANCE
LIGHT LH
FRONT SIDE MAKER
LIGHT RH
FRONT CLEARANCE
LIGHT RH
ABS ACTUATOR
FRONT TURN SIGNAL
LIGHT RH
CRUISE CONTROL
ACTUATOR
OXYGEN SENSOR SUB
(
FOR USA SPEC. )
TDCL (
E1 )
WASHER LEVEL SW EFI MAIN RELAY
CORNERING LIGHT RH
A/C PRESSURE SW
(HI GH PRESSURE )
AIR FLOW METER POWER STERRI NG
PRESSURE SW
NOISE FI LTER
(
FOR IGNI TION SYSTEM ) E4
E10
E12 2
2
BS1 4 E4
E7
E1 E5
EB EA I23
I33
E1 6
I32
E20
E20
E20
IK2 24
ED EC IK1
1 BY1
5
W±B
W±B
W±B
W±B
W±B
W±B
W±B
W±B
W± B W±B
W±B
W±B
W±B
W±B
W±B
W±B
W±B
W±B
W±B
W±B
W±B BR
BR
W±B BR
BR
BR
W±B BR
BR±B BR BR
BR
BR
W± B
W± B
W± B
W± B
W± B
W± B
W± B
W±B
W±B
BR
BR
BR
BR BR
BR
BR
W±B
BR BR
BR
( EO1 )
( E11 )
( E1 )
( EO2 )
I27BR
(
S1 )
( E1 )
NOISE FILTER (
FOR
IGNITION SYSTEM )W±B
W/ TRACTION SYSTEM
NOI SE FILTER
(
FOR DEFOGGER SYSTEM )
W±B
W±B
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567 8
EB1
EC ED D DCCCCD
CCCC
C IJ2 IJ2
IG2
EB1
C D C DC C CCC
DDCDDDDDCCCCC
ED
1 2
1
2 23
1 23
14
4 234 51
25
1346
2
B±O
B±W B±OB±Y
B± R
B± R
W
R± LBR
B± R B±Y W
L±R
B±Y LG
GR±Y B Y B
G±W L±Y
R± G P B± R
B± R
18 19 17 16 15 46 23 44 34
31 32 34 32 35 33 33 24 2 76 1 37B
B± Y
B±R W
L±R
W± B
W± B
BR
LG±BL±WV±R
G± YB± Y
B± O P
B±W B± O
BR
W
L±R
B±R
P
B±O
BR
BR
#30 #20 #40 #50 #60 THG ACMG THW A/C
B±R
B±R
B±R
EB1
Fro m
Spe ed Sen sor
< 21±7>
P± L
Y± L
V± Y
Y± G
W± Y Y±R
L±R
Y± B
Y± G L±R
L±R
BR
BR
65 63 42 64 43 38 39 40 58 57 41 45 66 A9
AIR FLOW METER
From Trac tion ECU
< 8±8>
From I gniter
< 1±6>
7P
E2 IDL2 VTA2
IDL1
VTA1
THA
VC KS
IGT
IGF
VT 01
VT 02
NEO
TR
IGSW
NS W
SP1
M±REL
BATT
ISC3
ISC1
ISC4
ISC2
+B1
+B I1
ISC
VALVEBR
R±BBR
Y± L
L±R
R
Y
L±R
L±R
L±R
BR
L±R
BR
BR
BR
BR
BR W
G
From Magnet ic
Cl ut ch Rel ay
< 22±1>
To A/ C Amp lif ie r
< 22±7>
E3
EGR GAS TEMP. SENSOR
E2
EFI WATER TEMP. SENSOR
S9
SUB THROTTL E
POSITI ON SENSOR T2
THROTTLE
POSITI ON SENSOR
BR
Engine Control
2LEXUSSC300
(
Cont ' d )
ENGI NE AND ECT ECU, ENGI NE ECU *
1: (
w/ Trac tion Control )
(
* 1)
( * 2)
( * 1)
( * 2)
(
* 1 ) *
2:
(
w/ o Tr a ct i o n Co nt r ol )
(
* 1 ) To Trac ti on
ECU< 8±8>
R±B
R
4311 8
B±O
BR (
* 3)
(
* 3) *
3: (
US A S pe c. )
* 4:
(
Ex . USA Spe c. )
E9 , E10 DC
BR
Front side of
intake manifold Rear side of
c ylinder head RH Rear side of
c ylinder head RH
C
C
C 1 2
1
2
2
1
C
C
C
C
C
C
D
D
C
C
C
C
D
D
C
D
C
D
D
20
77
27
7
25
26
22
21
80
79
4
69
4
6
29
20
28
19
17
V7
VSV (
for Int ake
Contr ol Valve )
V2
VSV
(
for EVAP )
V1
VSV
(
for EGR )
BY1
BY1
BY1 BY1
BR
R±B
(
* 4 )
W
(
* 4 )
B±R
BR±W
(
* 3 )
R±L
(
* 3
)
3142 1256
IK2
IK2
12
22
C
C
1
O3
OXYGEN SENSOR
MAIN No. 1
(
ON Front Side )
C48 71 61 75 74
1
O4
OXYGEN SENSOR
MAIN No. 2
(
ON Rear Side )
C
D
1 2
35 47
P2 0
POWER STEERING
PRESSURE SW
IK11
IJ1
IJ1
(SHIELDED )2341 C
C
1
1 49
50
D1 3
DI ST RI B UTOR
( SHIELDED )
EC
Front side of
intake manifold
G±Y G± R
8
14
K1
No. 1(
ON Fr ont Side )
KNOCK SENSOR
K2
No. 2 (
ON Rear Side ) BR BR
BR
W
W L
B Y
R R±G
P
W± B
W± B G±W
L±Y
GR±Y LG
B±Y
G±Y
BR
BR
BR
G1 G2 G± NE
#10
TT TE2 VF2 TE1 VF1 W STP E1 E1 1 E0 2 E01 DI FPC G1 G2 G± NE KNK1 KNK2 STA ACI S
PS OX2 OX1 HT OX3 EGR EVAP 39
G± R G±B
B±W BR± W
BR± W
BR
B±R
B±R
B±R
B±R
W
BR± W
W
R±L
BR BR
BR
R±L W
LG±B BR
BR
(
SHI ELDED )
(
SHI EL DED )
(
SHI ELDED )
( SHIELDED )
O8
OXYGEN SENSOR SUB
(
for California )
BR
BR
Y B
R± L
BR
(* 4)
(
* 4)
(A/ T )
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50
POWER SOURCE (Current Flow Chart)*1: USA
*2: CANADA
P18
P11
N2 N4 O2 P2 O8 P4 P6 R5 R4 P20
P14
226
154
192
154
190 68 154 90
202
202
P8
P7
184 94
O5 P5 P3
Parking Brake SW
Power Window Motor RH Power Window Motor LHOil Pressure SW
Power Seat Control SW
(for Driver's Seat)
Power Seat Control SW
(for Passenger's Seat)Power Seat ECU (Passenger's)Oxygen Sensor Sub
(for California)Power Seat Motor (for Driver's
Lumbar Support Control)O/D Main SW
Radio and Player Personal LightRadio and Player (w/ CD Player)Noise Filter
(for A/C System)Power Seat Motor (for Passenger's
Reclining Control)PPS ECU
Power Window Control SW RH
Power Window Master SW and
Door Lock Control SW LH
*Page Nos. of
Related Systems Parts
Code or
Location
CB or Fuse
50A DEFOG
30A DOOR
30A POWER
15A STOP
15A ECU±B
10A MIR±HTR
10A HEATER
20A TURN
20A WIPER
10A GAUGE
15A ECU±IG
7.5A ENGINE
7.5A IGN
15A CIG
7.5A RADIO No.2
15A TAIL
7.5A PANEL
7.5A ST
15A TEL
10A DOME
20A RADIO No.1
25A HAZ±HORN
30A EFI
7.5A ALT SENCING
15A HEAD LH*1
15A HEAD RH*1
15A HEAD LH±LWR*2
15A HEAD RH±LWR*2
15A HEAD LH±UPR
15A HEAD RH±UPR
60A HEATER
7.5A TRAC
15A SEAT±HTR
LocationP9 P12 P10 R2
Power Seat ECU (Driver's)Noise Filter
(for Defogger System)
216 126 216 208
122


* These are the page numbers of the first page on which the related system\
is shown.
The part indicated is located somewhere in the system, not necessarily o\
n the page indicated here.
[LOCATION](1): J/B No. 1 (See page 20)(2): R/B No. 2 (See page 19)(3): R/B No. 4 (See page 23)
20
19 22
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