1991 LEXUS SC400 check engine

OKNG
8Check Ignition Relay.
C
OK
P
C
OK
Remove ignition relay.
Check continuity between terminals of ignition relay
shown below.
(2) Apply battery voltage between terminals 3 and 6, 4and 5.
(2) Check continuity between terminals 1 and 2.
Replace ignition relay.
Check and repair harness or connector between
battery and ignition relay, ignition relay and igni-
ter.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±59
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NGOK
OKNG
9Disconnect igniter connector and check voltage between terminals IGT1, 2 of engine & ECT
ECU connector and body ground.
C
OK
PDisconnect igniter connector.
Connect engine & ECT ECU connector.
Measure voltage between terminals IGT1, 2 of engine
& ECT ECU connector and body ground when engine
is cranked.
Voltage: 0.5 ± 1.0 V(Neither 0 V nor 5 V)
Replace igniter .*1
10Check for Open and short in harness and connector in IGT signal circuit betwee\
n engine & ECT
ECU and igniter (See page IN±27).
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
*1: When diag. code 14 is displayed, replace the igniter with 5 wire harness. (extra wire is for tachometer). When diag.
code 15 is displayed, replace the igniter with 4 wire har-
ness
TR±60±
ENGINE TROUBLESHOOTING Circuit Inspection
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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. code isno longer detected.

Disconnect the EFI fuse (15 A) for 10 sec. or more, with IG switch OFF\
.
Initiate test mode (Connect terminal TE2 and E1 of check connector or TDCL with IG
switch OFF).
Start the engine and warm up with all ACC switch OFF.
After the engine is warmed up, let it idle for 3 min.
After performing the idling in , perform gradual acceleration with in th\
e range 1,300
1,700 rpm (centered around 1,500 rpm) with the A/C switch ON and D range fo\
r A/T
(5th for M/T).
(Take care that the engine speed does not fall below 1,200 rpm when shifting.\
Gradu-
ally depress the accelerator pedal and kept it. Steady so that engine br\
aking does not
occur).
Maintain the vehicle speed at 40±50 mph (64±80 km/h).
Keep the vehicle running for 1±2 min. after starting acceleration.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light\
up after approx. 60 sec. from the start of acceleration.
NOTICE: If the conditions in this test are not strictly followed, detection of t\
he malfunction will not be possible.
Malfunction: Main Oxygen Sensor Deterioration
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ENGINE TROUBLESHOOTING Circuit InspectionTR±61
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CIRCUIT DESCRIPTION (Cont'd)
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 confirming that diag.code is no longer detected.
DIAGNOSIS CODE DETECTION DRIVING PATTERN
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 ON), perform
gradual acceleration with in the range 1,300 ± 1,700 rpm (centered
around 1,500 rpm).
(Take care that the engine speed does not fall below 1,200 rpm when
shifting. Gradually depress the accelerator pedal and kept it. Steady so
that engine braking does not occur.)
Maintain the vehicle speed at 40 ± 50 mph (64 ± 80 km/h).
Keep the vehicle running for 1 ± 2 min. after starting acceleration.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light\
up af-
ter approx. 60 sec. from the start of acceleration.
NOTICE: If the conditions in this test are not strictly followed, detection of the malfunction will not be possible.
TR±63
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ENGINE TROUBLESHOOTING Circuit Inspection
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DIAGNOSTIC CHART
DIAGNOSTIC
CHART
WIRING DIAGRAM
HINT: If diag. code º21º is output, check the left bank main oxygen sens\
or circuit. If diag. code º28º is output, check the right bank main oxygen sensor circuit.
Check voltage of terminals HTL1, HTR1.
Check resistance of oxygen sensor heater.
Check and repair oxygen sensor heater circuit.
Check operation of oxygen sensor heater.
Check and replace ECU. Replace main oxygen sensor.
*: In this case, oxygen sensor can be deteriorated.
Replace main oxygen sensor.*
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ENGINE TROUBLESHOOTING Circuit InspectionTR±64
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OKNG
OKNG
INSPECTION PROCEDURE
1Disconnect the engine & ECT ECU connector, check voltage between terminals HTL1, HTR1 of
engine & ECT ECU connector and body ground.
C
OK
P(2) Connect the Check Harness A.(See page TR±30)
(2) Disconnect engine & ECT ECU connector.
(2) Turn ignition switch on.
Measure voltage beween terminals HTL1, HTR1 of en-
gine & ECT ECU connector and body ground.
Voltage: 10 ± 14 V
Go to step [3].
2Check main oxygen sensor heater.
C
OK
PDisconnect main oxygen sensor connector.
Measure resistance between terminals 1 and 2 of main
oxygen sensor connector.
Resistance: 5.1 ± 6.3
at 20 C (68 F)
Replace main oxygen sensor.
Check and repair harness or connector between
main relay and main oxygen sensor, main oxygen
sensor and engine & ECT ECU.
TR±65±
ENGINE TROUBLESHOOTING Circuit Inspection
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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.
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ENGINE TROUBLESHOOTING Circuit InspectionTR±66
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DIAGNOSTIC CHART
HINT: If diagnostic codes º22º (water temperature sensor circuit), º2\
4º (intake air temperature sensorcircuit) and º41º (throttle position sensor circuit) are output\
simultaneously, E2 (sensor ground)
may be open.
Check voltage of sensor.Check for momentary
interruption (See page TR±27).
Replace water temp. sensor.
Repair or replace harness or
connector.Check for open and short in harness and
connector between ECU and water temp.
sensor.
Check resistance of sensor.
Check and replace ECU.
WIRING DIAGRAM
aa
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±65
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