1991 LEXUS SC400 oxygen sensor

TERMINALS OF ENGINE & ECT ECU (Cont'd)
TerminalNo.SymbolConnectionTerminalNo.SymbolConnection
E10± 21NCOT/M Input Speed SensorE10 ± 51±
22±52HTL2LH Sub±Oxygen Sensor Heater
23SP2No.2 Speed Sensor for ECT53HTR2RH Sub±Oxygen Sensor Heater
24±54±
25G2LH (No.2) Cam Position Sensor55±
26G1RH (No.1) Cam Position Sensor56IGT2No.2 Igniter for RH Bank
27NEEngine Speed Sensor57IGT1No.1 Igniter for LH Bank
28VF2Check Connector58IGF1No.1 Igniter for LH Bank
29VF1Check Connector59IGF2No.2 Igniter for RH Bank
30±60±
31±61±
32ISC4ISC Valve62±
33ISC3ISC Valve63IDL2Sub±Throttle Position Sensor
34ISC2ISC Valve64IDL1Throttle Position Sensor
35ISC1ISC Valve65E2Sensor Ground
36* EGR4EGR Valve66KSAir Flow Meter
37* EGR3EGR Valve67OXR2
38* EGR2EGR Valve68OXL2LH Sub±Oxygen Sensor
39* EGR1EGR Valve69E1ECU Ground39* EGRVSV for EGR69E1ECU Ground
40±70±
41VCThrottle Position Sensor
Air Flow Meter71HTL1LH Main Oxygen Sensor
42VTA2Fuel Pump ECU72HTR1RH Main Oxygen Sensor
43VTA1A/C Magnet Clutch Relay73FPUVSV for Fuel Pressure Control
Value
44THWWater Temp. Sensor74* PA GVSV for EVAP
45THAIntake Air Temp. Sensor75±
46THGEGR Gas Temp. Sensor76NSWNeutral Start Switch
47OXR1RH Main Oxygen Sensor77STAStarter Relay
48OXL1LH Main Oxygen Sensor78STJCold Start Injector
49KNK2RH (No.2) Knock Sensor79E02Power Ground
50KNK1LH (No.1) Knock Sensor80E01Power Ground
Engine & ECT ECU Terminals
*USA spec. only
*  A/T only
FI±127EFI SYSTEM ± Electronic Control System (Engine & ECT ECU)
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SERVICE DATA (Cont'd)
Water temp.
sensorResistanceat ±20°C (±4 °F)
at 0 °C (32 °F)
at 20 °C (68 °F)
at 40 °C (104 °F)
at 60 °C (140 °F)
at 80 °C (176 °F)10 ± 20 k

4 ± 7 k

2 ± 7 k

0.9 ± 1.3 k

0.4 ± 0.7 k

0.2 ± 0.4 k

EGR gas
temp.
sensorResistanceat 50°C (112 °F)
at 100 °C (212 °F)
at 150 °C (302 °F)69 ± 89 k

12 ± 15 k

2 ± 4 k

Main oxygen
sensorHeater coil resistance5.1 ± 6.3

Sub±oxygen
sensorHeater coil resistance5.1 ± 6.3

ECUHINT:

Perform all voltage and resistance measurements with the ECU connected.

Verify that the battery voltage in 11 V or above with the ignition switch is ON.
Voltage
TerminalsConditionSTD voltage (V)
BATT ± E1±10 ± 14
IGSW
+B ± E1
+B1
IG SW ON10 ± 14
VC ± E2±4.0 ± 6.0
IDL1E2
Throttle (or sub±throttle) valve fully closed1 or lessIDL1
IDL2 ± E2
IG SW ONThrottle (or sub±throttle) valve fully open10 ± 14
VTA1E2
Throttle (or sub±throttle) valve fully closed0.1 or lessVTA1
VTA 2 ± E2
Throttle (or sub±throttle) valve fully open3.0 ± 6.0
KS ± E1IdlingPulse generation
THA ± E2
THW±E2Idling
Intake air temp. 20
°C (68 °F)1.0 ± 3.0
THW ± E2IdlingEngine coolant temp. 80 °C (176 °F)0.1 ± 1.0
STA ± E1Cranking6.0 or more
#10
#20
E01IG SW ON10 ± 14#20
#30
#40±
E01
E02IdlingPulse generation
IGT1
IGT2
± E1IdlingPulse generation
FI±138EFI SYSTEM
± Service Specifications
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TORQUE SPECIFICATIONS
Part tightenedNVmkgf Vcmft Vlbf
Fuel line Union bolt type
Flare nut type2930022
Fuel pipe X Delivery pipe39400 29
Fuel pump bracket X Fuel tank5.455 48 in.Vlbf
Fuel pump set plate X Fuel tank3.940 35 in. Vlbf
Fuel tank X Body25250 18
Fuel sender gauge X Fuel tank2.930 26 in. Vlbf
Fuel inlet pipe X Fuel tank2.930 26 in. Vlbf
Fuel tank main tube X Fuel tank29300 22
Fuel tank return tube X Fuel tank29300 22
Fuel tank evaporation vent tube X Fuel tank29300 22
Air flow meter X Air cleaner case10100 7
Cold start injector X Air intake chamber7.880 69 in. Vlbf
Cold start injector tube X Cold start injector15150 11
Air intake chamber X Intake manifold18185 13
EGR pipe X Air intake chamber18185 13
EGR pipe X RH cylinder head18185 13
Cold start injector tube X RH Delivery pipe15150 11
Throttle body X Air intake chamber18185 13
Fuel return pipe X Fuel pressure regulator35360 26
Fuel pressure regulator X RH delivery pipe29300 22
Delivery pipe X Intake manifold18185 13
Fuel inlet hose X LH delivery pipe39400 29
for SST33340 24
ISC valve X Air intake chamber18185 13
Cold start injector time switch X Front water by±pass joint34350 25
Water temperature sensor X Front water by±pass joint20200 14
Water inlet housing X Water pump18185 13
EGR gas temperature sensor X EGR valve adaptor20200 14
EGR valve adaptor X Air intake chamber18185 13
EGR valve X EGR valve adaptor18185 13
Knock sensor X Cylinder block44450 33
Intake manifold X Cylinder head18185 13
Main oxygen sensor X Exhaust manifold44450 33
Sub±oxygen sensor X Exhaust manifold4445033
FI±142EFI SYSTEM ± Service Specifications
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REMOVAL OF OIL PUMP
(See Components on page LU±8)
HINT: When repairing the oil pump, the oil pan and strainer
should be removed and cleaned.
1. REMOVE ENGINE WITH TRANSMISSION (See pages EM±118 to 128)
2. SEPARATE ENGINE AND TRANSMISSION (See pages EM±129 to 130)
3. INSTALL ENGINE TO ENGINE STAND FOR REMOVAL
4. REMOVE TIMING BELT (See steps 8 to 35 on pages EM±36 to 43)
5. REMOVE NO.2 IDLER PULLEY, NO.1 IDLER PULLEY AND CRANKSHAFT TIMING PULLEY
(See steps 36 to 38 on page EM±44)
6. REMOVE OIL DIPSTICK AND GUIDE (a) Remove the mounting bolt.
(b) Pull out the dipstick guide together with dipstick guide.
(c) Remove the O±ring from the dipstick guide.
7. REMOVE BRACKET OF MAIN OXYGEN SENSOR CONNECTOR FROM NO.1 OIL PAN
Remove the bolt, and disconnect the connector bracket.
8. REMOVE OIL LEVEL SENSOR (a) Disconnect the level sensor connector.
(b) Remove the four mounting bolts, and disconnect theengine wire bracket.
(c) Remove the level sensor.
(d) Remove the gasket from the level sensor.
9. REMOVE NO.2 OIL PAN (a) Remove the twelve mounting bolts and two nuts.
±
LUBRICATION SYSTEM Oil PumpLU±9
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8. INSTALL OIL LEVEL SENSOR(a) Install a new gasket to the level sensor.
(b) Install the level sensor with the four bolts.
Torque: 5.4 N Vm (55 kgf Vcm, 48 in. Vlbf)
HINT: Use bolts 16 mm (0.63 in.) in length.
(c) Connect the level sensor connector.
9. INSTALL BRACKET OF MAIN OXYGEN SENSOR CONNECTOR TO NO.1 OIL PAN
Install the connector bracket with bolt.
10. INSTALL OIL DIPSTICK GUIDE AND DIPSTICK (a) Install a new O±ring to the dipstick guide.
(b) Apply soapy water to the O±ring.
(c) Push in the dipstick guide into the guide hole of the No.1
oil pan.
(d) Install the engine wire bracket and dipstick guide with bolt.
(e) Install the oil dipstick.
11. INSTALL CRANKSHAFT TIMING PULLEY, NO.1 IDLER PULLEY AND NO.2 IDLER PULLEY
(See steps 1 to 3 on pages EM±46 and 47)
12. INSTALL TIMING BELT
(See steps 4 to 35 on pages EM±47 to 56)
13. REMOVE ENGINE STAND FROM ENGINE
14. ASSEMBLE ENGINE AND TRANSMISSION (See pages EM±165 and 166)
15. INSTALL ENGINE WITH TRANSMISSION (See pages EM±167 to 177)
±
LUBRICATION SYSTEM Oil PumpLU±19
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If a malfunction code is displayed during the diagnostic code check in tes\
t mode, check the circuit for that code
listed in the table below (Proceed to the page given for that circuit).
Tro ble Area
ºCHECKº EngineWarning Light *
Memory*See Page
Trouble AreaNormal
ModeTest
Mode
±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
w Open or short in engine speed sensor, No. 1, No. 2
cam position sensor circuit.
w Engine speed sensor
w No. 1, No. 2 cam position sensor
w Starter
w ECU
ONN.A.TR±48
w Open or short in engine speed sensor circuit.w Oen or short in engine s eed sensor circuit.
w Engine speed sensor
ONN.A. Engine s eed sensor
w ECU
ONN.A.
w Open or short in engine speed sensor circuit.g
w Mechanical system malfunction (skipping teeth of
ti itiming
wbelt belt stretched)N.A.ONTR 52wbelt, belt stretched)
wEngine speed sensor
TR±52
w Engine s eed sensor
w ECU
w Mechanical system malfunction (skipping teeth ofw Mechanical system malfunction (ski ing teeth of
wtiming belt, belt stretched)ONNAwtiming belt, belt stretched)
w No. 1, No. 2 cam position sensorONN.A. No. 1, No. 2 cam osition sensor
w ECU
w Open or short in IGF1 circuit from igniter No.
1±ECU.
w Igniter No. 1
w ECU
ONN.A.TR±54
w Open or short in IGF2 circuit from igniter No.
2±ECU.
w Igniter No. 2
w ECU
ONN.A.TR±54
w ECUONN.A.XTR±61
w Open or short in heater circuit of main oxygen sen-
sor.
w Main oxygen sensor heaterONN.A.w Main oxygen sensor heater
w ECU
TR±62
w Main oxygen sensor circuit
w
Main oxygen sensorONONw Main oxygen sensor
*1, 2: See page TR±20.
±
ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±15
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ºCHECKº Engine
Tro ble Area
CHECK Engine
Warning Light *
Memory*See PageTrouble AreaNormal
ModeTest
ModeMemory* See Page
w Open or short in water temp. sensor circuit.
w Water temp. sensor
w ECU
ONONTR±68
w Open or short in intake air tempsensor circuitOFFw Open or short in intake air temp. sensor circuit.
w Intake air tempsensor
OFF
ONTR 72w Intake air temp. sensor
ECUON*3
ONTR±72
w ECUON*3
w Open or short in main oxygen sensor circuit.w Oen or short in main oxygen sensor circuit.
w Main oxygen sensor
Main oxygen sensor
w Ignition systemgy
w Water temp. sensor
w Open or short in injector circuit.w Oen or short in injector circuit.
w Fuel line pressure
(injector blockage)w Fuel line ressure (injector blockage)
w Air flow meter (air intake)ONONTR±74 Air flow meter (air intake)
w Engine ground bolt loose

gg
w Foreign object caught in valve
w Fuel line pressure (injector leak, blockage)w Fuel line ressure (injector leak, blockage)
w Mechanical system malfunction Mechanical system malfunction
w(skipping teeth of timing belt)(g g)
w Ignition system
w Open or short in heater circuit of sub±oxygen sen-
sor.
w Sub±oxygen sensor heaterONN.A.w Sub±oxygen sensor heater.
w ECU
TR±82
w Open or short in sub±oxygen sensor circuit.
TR 82
w Oen or short in sub oxygen sensor circuit.
w Sub±oxygen sensor
ONON Sub oxygen sensor
w ECU
w Same as (1) of Code No. 21ONN.A.
TR 62w Same as (2) of Code No. 21ONONTR±62
w Same as (1) of Code No. 27ONN.A.
TR 82w Same as (2) of Code No. 27ONONTR±82
*1, 2, 3: See page TR±20.
±
ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±17
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Diag. Code 21, 28Main Oxygen Sensor Circuit
CIRCUIT DESCRIPTION
To obtain a high purification rate for the CO, HC and NOx components of th\
e exhaust gas, a three±way
catalyst is used, but for most efficient use of the three±way catalyst, the air±fuel ratio must be \
precisely
controlled so that it is always close to the stoichiometric air±fuel \
ratio.
The oxygen sensor has the characteristic whereby its output voltage chan\
ges suddenly in the vicinity of
the stoichiometric air±fuel ratio. This characteristic is used to det\
ect the oxygen concentration in the ex-
haust gas and provide feedback to the computer for control of the air±\
fuel ratio.
When the air±fuel ratio becomes LEAN, the oxygen concentration in the exh\
aust increases and the oxygen
sensor informs the ECU of the LEAN condition (small electromotive force: O V)\
.
When the air±fuel ratio is RICHER than the stoichiometric air±fuel\
ratio the oxygen concentration in the
exhaust gas is reduced and the oxygen sensor informs the ECU of the RICH condition (large electromotive
force: 1V).
The ECU judges by the electromotive force from the oxygen sensor whether th\
e air±fuel ratio is RICH or
LEAN and controls the injection time accordingly. However, if malfunction of the oxygen sensor causes
output of abnormal electromotive force, the ECU is unable to perform accurate \
air±fuel ratio control.
The main oxygen sensors include a heater which heats the Zirconia element. The heater is controlled by
the ECU. When the intake air volume is low (the temperature of the exhaust\
gas is low) current flows to
the heater to heat the sensor for accurate oxygen concentration detectio\
n.
Code No.Diagnostic Code Detecting ConditionTrouble Area
(1) Open or short in heater circuit of main
oxygen sensor for 0.5 sec. or more.

Open or short in heater circuit of main oxygen sen-
sor.

Main oxygen sensor heater

ECU
21 V
28
(2) Main oxygen sensor signal voltage is reduced to be-
tween 0.35 V and 0.70 V for 60 sec. under conditions
(a) ~ (d). (2 trip detection logic)*
(a) Coolant temp.: Between 70 5C (158 5F) and 95 5C
(203 5F).
(b) Engine speed: 1,500 rpm or more.
(c) Load driving (EX. ECT in 4th speed, A/C ON, Flat road, 50 mph (80km/h)).
(d) Main oxygen sensor signal voltage:
Alternating above and below 0.45 V.

Main oxygen sensor circuit

Main oxygen sensor
*: See page TR±21.
HINT : Diag. code 21 is for the left bank main oxygen sensor circuit. Diag. co\
de 28 is for the right bank main oxy-
gen sensor circuit.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±62
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