oxygen sensor LEXUS SC400 1991 Service Owners Manual

OKNG
3Check voltage between terminals HTL1, HTR1 of engine & ECT ECU connector and \
body
ground.
C
OK
Hint
P(1) Connect engine & ECT ECU connector.
(2) Warm up engine to normal operating temperature.
Measure voltage between terminals of HTL1, HTR1 of
engine & ECT ECU connector and body ground, when
engine is idling and racing at 4,000 rpm.
In the 4,000 rpm racing check, continue engine racing
at 4,000rpm for approx. 20 seconds or more.
Replace main oxygen sensor.**: In this case, oxygen sensor can be deteriorated.
Check and replace engine & ECT ECU.
Reference | INSPECTION USING OSCILLOSCOPE
w With the engine racing (4,000 rpm) measure between
terminals OXL1, OXR2 and E1 of engine & ECT ECU.
HINT: The correct waveform appears as shown in the
illustration on the left, oscillating between approx.
0.1 V and 0.9 V
If the oxygen sensor is deteriorated, the amplitude
of the voltage is reduced as shown on the left.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±66
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Diag Code

25Air±Fuel Ratio Lean Malfunction
Diag. Code
26Air±Fuel Ratio Rich Malfunction
CIRCUIT DESCRIPTION
Refer to page TR±62 for the circuit description.
Code No.Diagnostic Code Detecting ConditionTrouble Area
(1) Main oxygen sensor voltage is 0.45 V or less (lean)
for 90 sec. under conditions (a) and (b).
(2 trip detection logic)*
(a) Coolant temp.: 60 5C (140 5F) or more.
(b) Engine speed: 1,500 rpm or more.
Open or short in main oxygen sensor circuit

Main oxygen sensor

Ignition system

Water temp. sensor
25 V
26
(2) Main oxygen sensor voltage is alternating above and below 0.45 V at 5 times par
second or more under conditions (a) and (b).
(2 trip detection logic)*
(a) Engine speed: Idling
(b) Coolant temp.: Between 60 5C (140 5F)
and 95 5C (203 5F)

Open or short in injector circuit.

Fuel line pressure (injector blockage)

Air flow meter (air intake)

Engine ground bolt loose

Foreign object caught in valve
(3) Difference of air±fuel ratio feedback compensation
value between right and left banks is more than 10
percentage for 30 sec. or more under conditions (a)
and (b).
(2 trip detection logic)*
(a) Engine speed : 2,000 rpm or more.
(b) Coolant temp.: Between 60 5C (140 5F)
and 95 5C (203 5F)

Fuel line pressure (injector leak, blockage)

Mechanical system malfunction
(skipping teeth of timing belt)

Ignition system
*: See page TR±21.
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CIRCUIT DESCRIPTION (Cont'd)
DIAGNOSIS CODE DETECTION DRIVING PATTERN
Purpose of the driving pattern.
(a) To simulate diag. code detecting condition after diag. code is recorded.
(b) To check that the malfunction is corrected when the repair is completed c\
onfirming that diag. code is no longer detected.
Malfunction: Open or Short in Main Oxygen Sensor

Initiate test mode (See page TR±12).
Start engine and warm up.
After engine is warmed up, let it idle for 3 min.
Perform quick racing to 4,000 rpm three times by accelerator pedal.
After performing the racing in (4), perform racing at 2,000 rpm for 90\
sec.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light up after 90 sec. from the start of racing.
NOTICE: If the conditions in this test are not strictly followed, detection of t\
he malfunction will not be possible.
TR±75±
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DIAGNOSTIC CHART
DIAGNOSTIC
CHART
WIRING DIAGRAM
Refer to page TR±64 for the WIRING DIAGRAM.
Check and replace ECU. Repair or replace harness or
connector.
Check compression Check and replace ECU.
Does malfunction disappear when a good main
oxygen sensor is installed?
Check compression.
Check each item found to be a possible cause
of problem. Check for open and short in harness and
connector.
Check voltage of terminal OX.
Check voltage of terminal VF.
Replace main oxygen sensor. Repair or replace.
Does malfunction disappear when a good main
oxygen sensor is installed? Check each item found to be a possible cause
of problem. Replace main oxygen sensor.
Repair or replace.
Repair or replace.
Repair or replace.
TR±77±
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NG
Type ING
Type II
NG
OK
INSPECTION PROCEDURE
1Check voltage between terminals VF1, VF2 and E1 of check connector.
C
P(2) Warm up engine at normal operating temperature.
(2) Connect terminals TE1 and E1 of check connector.
(2) Connect positive prove to terminal VF1, VF2 and negative prove to terminal E1 of check connector.
(2) Warm up the oxygen sensor by running engine at 2,500 rpm for about 2 minutes.
(2) Then, maintaining engine at 2,500 rpm, count how many times needle of voltmeter fluctuates between
0 and 5 V
Result:
Go to step [7].
2Check voltage beween terminals OX1, OX2 and E1 of check connector.
C
OK
Hint
PWarm up engine at normal operating temperature.
Measure voltage between terminals OX1, OX2 and E1
of check connector when sngine is suddenly raced to full
throttle.
The Voltage should be 0.5 V or higher at least once.
Perform inspection within 1 second
Go to step [7].
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ENGINE TROUBLESHOOTING Circuit InspectionTR±78
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OKNG
OKNG
OKNG
NOYES
3
Check for open and short in harness and connector between engine & ECT ECU an\
d main oxy-
gen sensor, engine & ECT ECU and check connector (See page IN±27).
Repair or replace harness or connector.
4Check each item found to be a possible cause of problem.
Check each circuit found to be a possible cause of trouble according to the results of the check in \
1 or
2 . The numbers in the table below show the order in which the checks sho\
uld be preformed.
TR±132
TR±6
TR±51
TR±13
TR±114
TR±88
TR±68
TR±72
Repair or replace.
5Check comparession (See page EM±30).
Repair or replace.
6Does malfunction disappear when a good main oxygen sensor is installed?
Replace main oxygen sensor.
check and replace engine & ECT ECU.
TR±79±
ENGINE TROUBLESHOOTING Circuit Inspection
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OKNG
OKNG
NOYES
7Check each item found to be a possible cause of problem.
Check each ciruit found to be a possible cause of trouble according to the re\
sults of the check in 1. The
numbers in the table below show the order in the which the checks should be per\
formed.
TR±132
TR±6
TR±51
TR±13
TR±114
TR±88
TR±68
TR±72
TR±72
Repair or replace.
8Check compression (See page EM±30).
Repair or replace.
9Does malfunction disappear when a good main oxygen sensor is installed?
Replace main oxygen sensor.
Check and replace engine & ECT ECU.
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ENGINE TROUBLESHOOTING Circuit InspectionTR±80
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Diag. Code 27, 29Sub±Oxygen Sensor Circuit
CIRCUIT DESCRIPTION
The sub±oxygen sensor is installed on the exhaust pipe. Its construction\
and operation is the same as the main
oxygen sensor on page TR±62.
Code No.Diagnostic Code Detecting ConditionTrouble Area
(1) Open or short in heater circuit of sub±oxygen
sensor for 0.5 sec. or more.

Open or short in heater circuit of sub±oxygen
sensor

Sub±oxygen sensor heater.

ECU
27


29(2) Main oxygen sensor signal is 0.45 V or more and sub±oxygen sensor signal is 0.45 V or less
under sonditions (a) and (b).
(2 trip detection logic) *
(a) Coolant temp.: 80 5C (176 5F) or more.
(b) Accel. pedal: Fully depressed for 2 sec. or more.

Open or short in sub±oxygen sensor circuit.

Sub±oxygen sensor

ECU
*: See page TR±21.
HINT: Diag. code 27 is for the left bank sub±oxygen sensor circuit.
Diag. code 29 is for the right bank sub±oxygen sensor circuit.
TR±82
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CIRCUIT DESCRIPTION (Cont'd)
DIAGNOSIS CODE DETECTION DRIVING PATTERN
Purpose of the driving pattern.
(a) To simulate diag. code detecting condition after diag. code is recorded.
(b) To check that the malfunction is corrected when the repair is completed co\
nfirming that diag. codeis no longer detected.
Malfunction: Open or Short in Sub±Oxygen Sensor

Initiate test mode (See page TR±12).
Start engine and warm up.
After engine is warmed up, let it idle for 3 min.
With the A/C ON and the transmission in D range (O/D OFF), drive at 40 ±\
60 mph (64±96
km/h) for 6 min.
After the driving in , stop the vehicle.
Once the vehicle is stopped, within the next minute apply acceleration w\
ith the throttle
fully open for 4 sec.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light\
up after full acceleration for 4 sec.
NOTICE: If the conditions in this test are not strictly followed, detection of the\
malfunction will not be possible.
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DIAGNOSTIC CHART
DIAGNOSTIC
CHART
HINT:
wWhen other codes are output in addition to 27 and 29 at the same time, check the ci\
rcuits for other
codes first.
w If diag. code 27 is displayed, check left bank sub±oxygen sensor circ\
uit, and if 29 is displayed,
check right bank sub±oxygen sensor circuit.
WIRING DIAGRAM
Check voltage of terminals HTL2, HTR2.
Check resistance of sub±oxygen sensor heater.
Check and repair sub±oxygen sensor heater
circuit.
Check operation of sub±oxygen sensor heater.
Check and replace ECU. Replace main oxygen sensor.
*: In this case, oxygen sensor can be deteriorated.
Replace main oxygen sensor.*
TR±84±
ENGINE TROUBLESHOOTING Circuit Inspection
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