1991 LEXUS SC400 oxygen sensor

(b) Install the exhaust manifold with the eight new nuts.Uniformly tighten the nuts in several passes.
Torque: 39 N Vm (400 kgf Vcm, 29 ft Vlbf)
(c) Install the main oxygen sensor.
Torque: 44 N Vm (450 kgf Vcm, 33 ft Vlbf)
(d) Install the heat insulator with the three bolts.
3. INSTALL CYLINDER HEADS
A. Place cylinder heads on cylinder block (a) Place two new cylinder head gaskets in position on thecylinder block.
HINT: On the rear side of the cylinder head gasket are
painted marks to distinguish the LH and RH banks, a white
painted mark for the RH bank and a yellow painted mark for
the LH bank.
NOTICE: Be careful of the installation direction.
(b) Place the two cylinder heads in position on the cylinder
head gaskets.
EM±92
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ENGINE MECHANICAL Cylinder Heads
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B. Install cylinder head boltsHINT:
wThe cylinder head bolts are tighten in two progressive
steps (steps (c) and (e)).
w If any one of the cylinder head bolts broken or deformed,
replace it.
(a) Apply a light coat of engine oil on the threads and under
the heads of the cylinder head bolts.
(b) Te mp o ra rily in sta ll th e twe n ty pla te wa sh e rs an d cylinder head bolts.
(c) Uniformly tighten the ten cylinder head bolts on one side
of the cylinder head in several passes in the sequence
shown, then do the other side as shown.
Torque: 39 N Vm (400 kgf Vcm, 29 ft Vlbf)
If any one of the bolts does not meet the torque specification,
replace the bolt.
(d) Mark the front of the cylinder head bolt head with paint.
(e) Retighten the cylinder head bolts 90 ° in the numerical
order shown.
(f) Check that the painted mark is now at a 90 ° angle to
front.
4. CONNECT MAIN OXYGEN SENSOR CONNECTORS Connect the RH and LH oxygen sensor connector.
5. INSTALL CIRCULAR PLUGS (a) Place two new circular plugs in position on the cylinderheads, facing the cup side forward.
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ENGINE MECHANICAL Cylinder HeadsEM±93
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Main Oxygen Sensors
INSPECTION OF MAIN OXYGEN
SENSORS
1. WARM UP ENGINEAllow the engine to warm up to normal operating tempera-
ture.
2. INSPECT FEEDBACK VOLTAGE Connect the positive (+) probe of a voltmeter to terminal VF1
(for No.1) or VF2 (for No.2) of the check (ºDIAGNOSISº) con-\
nector, and negative (±) probe to terminal E1. Perform the
test as follows described on the next page.
HINT: Use SST when connecting between terminals TE1 and
E1 of the check connector.
SST 09843±18020
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EFI SYSTEM Electronic Control System (Main Oxygen Sensors)FI±73
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Replace the ECU
Zero againAfter replacing
the oxygen sensor
Normal
8 times
or moreZero
Check the number of times the voltmeter needle fluctuates in 10 seconds
Zero
8 times or more
Warm up the oxygen sensors with the engine at 2,500 rpm
for approx. 120 seconds
Connect terminals TE1 and E1 of the check connector.
And maintain engine at 2,500 rpm
Warm up the engine sensors with the engine at 2,500 rpm
for approx. 120 seconds. And maintain engine at 2,500 rpm.
Check the number of times the voltmeter needle
fluctuates in 10 seconds.
Less than 8 times
Disconnect terminals TE1 and E1 of the check connector.
And maintain engine at 2,500 rpm.
Measure voltage between terminals VF1 (VF2) and E1.
Less than 8 times
More than 0V
0V
Normal code, code
Nos. 21, 25, and 26Malfunction code(s)
(Ex. code Nos. 21, 25 and 26
Read and record diagnostic codes. (See TR section)
Repair the relevant diagnostic code
Disconnect terminals TE1 and E1 of the check connector.
And maintain engine at 2,500 rpm.
Read and record diagnostic codes. (See TR section)
Malfunction code(s)
(Ex. code Nos. 21, 25 and 26
Normal code, code
Nos. 21, 25, and 26
Repair the relevant diagnostic code
FI±74±
EFI SYSTEM Electronic Control System (Main Oxygen Sensors)
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Measure voltage between terminals VF1 (VF2) and E1.
Disconnect terminals TE1 and E1 of the check connector.
And maintain engine at 2,500 rpm.
Measure voltage between terminals VF1 (VF2) and E1.
Disconnect the PCV hose.
0V
5V
More than 0V
Repair (Over rich)
Disconnect the water temp. sensor connector and connect
resistor with a resistance of 4 ± 8 kW or another coded water
temp. sensor.
Connect terminals TE1 and E1 of the check connector.
Warm up the oxygen sensors with the engine at 2,500 rpm for
approx. 120 seconds, and maintain engine at 2,500 rpm
Measure voltage between terminals VF1 (VF2) and E1.
Replace the oxygen sensor.Repair (Over lean)
5V
0V
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EFI SYSTEM Electronic Control System (Main Oxygen Sensors)FI±75
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Sub±Oxygen Sensor (USA Spec. only)
COMPONENTS FOR REMOVAL AND
INSTALLATION
FI±76±
EFI SYSTEM Electronic Control System (Sub±Oxygen Sensor (USA Spec. only))
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INSPECTION OF SUB±OXYGEN SENSOR
1. INSPECT SUB±OXYGEN SENSOR(a) Cancel diagnostic code. (See TR section)
(b) A llo w th e en g in e to wa rm up to no rma l op e ra tin gtemperature.
(c) Drive for 5 minutes or more between 80km/h (50 mph) and 100 km/h (62 mph) in ºDº range.
(d) Following the conditions in step (c), press fully on the
accelerator pedal for 2 seconds or more.
HINT: Do not exceed 100 km/h (62 mph), or diagnostic code
will be cancelled.
(e) Stop the vehicle, and turn the ignition switch to OFF.
(f) Carry out steps (b), (c) and (d) again to test acceleration.
If code No. 27 reappears again, check the sub±oxygen sen-
sor circuit. If the circuit is normal, replace the sub±oxygen
sensor.
2. DISCONNECT CABLE FROM NEGATIVE TERMINAL OF BATTERY
CAUTION: Turn the ignition switch to ºLOCKº. Discon-
nect the cable from the negative (±) terminal of the bat-
tery. Wait at least 20 seconds before proceeding with
work.
3. REMOVE TRANSMISSION SHIFT LEVER KNOB (A/T)
(a) Push down the lever cover.
(b) Remove the two screws and shift lever knob.
(c) Remove the lever cover.
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EFI SYSTEMFI±77Electronic Control System (Sub±Oxygen Sensor (USA Spec. only))
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4. (A/T)
REMOVE CUP HOLDERUsing a screwdriver, pry out the rear side of the cup holder.
Remove the cup holder.
5. REMOVE UPPER REAR CONSOLE PANEL Using a screwdriver, pry out the console panel.
6. (A/T)
REMOVE UPPER CONSOLE PANEL (a) Remove the six mounting screws.
(b) Using a screwdriver, pry out the console panel.
7. DISCONNECT SUB±OXYGEN SENSOR CONNECTOR
8. INSPECT HEATER RESIST ANCE OF SUB±OXYGEN
SENSOR
Using an ohmmeter, measure the resistance between the ter-
minals +B and HT.
Resistance: 5.1±6.3
at 20 5C (68 5F)
FI±78±
EFI SYSTEM
Electronic Control System (Sub±Oxygen Sensor (USA Spec. only))
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