relay LEXUS SC300 1991 Service Repair Manual

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±
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DIAGNOSTIC CHART
HINT: When other codes are output in addition to 27 at the same time, check the ci\
rcuits for othercodes first.
WIRING DIAGRAM
Check voltage between terminal HT.
Check resistance of sub±oxygen sensor
heater.
Check for open and short in harness and
connector between EFI main relay and ECU.
Check and replace ECU.
Check operation of sub±oxygen sensor
heater.
Check and replace ECU.
Replace sub±oxygen sensor.
Repair or replace harness or
connector.
Replace sub±oxygen sensor.*
*: In this case, oxygen sensor can bedeteriorated.
TR±78±
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OKNG
NGOK
3Check for open and short in harness and connector between EFI main relay and engine (& ECT)
ECU (See page IN±27).
Repair or replace harness or connector.
Check and replace engine (& ECT) ECU.
4Check voltage between terminal HT of engine (& ECT) ECU connector and \
body ground.
C
OK
PWarm up engine to normal operating temperature.
Measure voltage between terminal HT of engine (&
ECT) ECU connector and body ground, when engine is
idling and racing at 3,500 rpm.
Replace sub±oxygen sensor.* *: In this case, oxygen sensor can be deteriorated.
Check and replace engine (& ECT) ECU.
TR±80±
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NGOK
OKNG
INSPECTION PROCEDURE
1Disconnect the engine & ECT ECU connector.
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 between terminals HTL2, HTR2 of en-
gine & ECT ECU connector and body ground.
Voltage: 10 ± 14 V
Go to step [3].
2Check sub±oxygen sensor heater.
C
OK
PDisconnect sub±oxygen sensor connector.
Measure resistance between terminals 1 and 2 of sub±
oxygen sensor connector.
Resistance: 5.1 ± 6.3
20 C (68 F)
Replace sub±oxygen sensor.
Check and repair harness or connector between
main relay and sub±oxygen sensor, sub±oxygen
sensor and engine & ECT ECU.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±85
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WIRING DIAGRAM
Check for the test mode.
Check for open in harness and connector
between ECU and relay.Repair or replace harness or
connector.
Proceed to next circuit inspection shown
on matrix chart (See page
TR±39).
Check and replace ECU.
Diag. Code 43Starter Signal Circuit
CIRCUIT DESCRIPTION
When the engine is cranked, the intake air flow is slow, so fuel vaporization is poor. A rich mixture is therefore
necessary in order to achieve good startability. While the engine is being cranked, the battery voltage is applied
to terminal STA of the ECU. The starter signal is mainly used to increase the fuel inj\
ection volume for the starting
injection control and after±start injection control.
DTC No.DTC Detecting ConditionTrouble Area
43No starter signal to ECU.

Open or short in starter signal circuit.

Open or short in ignition switch or starter
relay circuit.

ECU
DIAGNOSTIC CHARTDIAGNOSTIC CHART
HINT: This diagnostic chart is based on the premise that the engine is cranke\
d normally. If the engine is not
cranked, proceed to the matrix chart of problem symptoms on page TR±39.
TR±96
±
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INSPECTION PROCEDURE
Check output condition of diag. code 43
Setting the test mode.
6. Turn ignition switch OFF.
7. Connect terminals TE2 and E1 of TDCL.
8. Turn ignition switch ON.(Don't start the engine)
9. Connect terminals TE1 and E1 of TDCL.
Check if code ª43º is output by the ªCHECKº en-
gine warning light.
Code ª43º is output.
Start the engine.
Check if the code ª43º disappear.
Code ª43º is not output.
Proceed to next circuit inspection shown on
matrix chart (See page
TR±39).
Check for open in harness and connector between engine (& ECT) ECU
and starter relay (See page IN±27)
Repair or replace harness or connector.
Check and replace engine (& ECT) ECU.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±97
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Diag. Code 43Starter Signal Circuit
CIRCUIT DESCRIPTION
When the engine is cranked, the intake air flow is slow, so fuel vaporization is poor. A rich mixture is therefore
necessary in order to achieve good startability. While the engine is being cranked, the battery voltage is applied
to terminal STA of the ECU. The starter signal is mainly used to increase the fuel inj\
ection volume for the starting
injection control and after±start injection control.
Code No.Diagnostic Code Detecting ConditionTrouble Area
43No starter signal to ECU

Open or short in starter signal circuit.

Open or short in ignition switch or main relay
circuit.

ECU
DIAGNOSTIC CHARTDIAGNOSTIC CHART
HINT: This diagnostic chart is based on the premise that the engine is cranked nor\
mally. If the engine is not
cranked, proceed to the matrix chart of problem symptoms on page TR±35.
Check for the test mode.
Check for open in harness and connectors
between ECU and relay.
Check and replace ECU. Proceed to next circuit inspection shown
on matrix chart (See page
TR±35).
Repair or replace harness or
connector.
WIRING DIAGRAM
TR±100±
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NGOK
OKNG
v
INSPECTION PROCEDURE
1Check output condition of diag. code 43.
C
OK
P
OK
C
Setting the test mode.
(2) Turn ignition switch OFF.
(2) Connect terminals TE2 and E1 of TDCL.
(2) Turn ignition switch ON.(Don't start the engine)
(2) Connect terminals TE1 and E1 of TDCL.
Check if code ª43º is output by the ªCHECKº engine
warning light.
Code ª43º is output.
Start the engine.
Check if the code ª43º disapears.
Code ª43º is not output.
Proceed to next circuit inspection shown on maxtric
chart (See page TR±35).
2Check for open in harness and connectors between engine & ECT ECU and st\
arter relay
(See page IN±27).
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±101
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DIAGNOSTIC CHART
Check voltage of VSV for EGR Power
source.
Check resistance of VSV for EGR.
Repair or replace harness or
connector.
Replace VSV for EGR.
Check for open and short in harness and
connector between EFI main relay and ECU.
Check and replace EGR.
Check EGR system (See page EC±12).
Check resistance of EGR gas temp. sensor.
Check and replace EGR.
Check for open in harness and connector
between EGR gas temp, sensor and ECU.
Repair EGR system.
Replace EGR gas temp. sensor.
Repair or replace harness or
connector.
TR±106±
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NGOK
OKNG
OKNG
INSPECTION PROCEDURE
1Check voltage between terminal EGR of ECM connector and body ground.
C
OK
P1. Connect the Check Harness A. (See page TR±34).
2. Warm up engine to normal operating temperature.
Measure voltage between terminal EGR of engine (&
ECT) ECU connector and body ground.
Voltage:
Go to step
.
2Check resistance between terminals of VSV for EGR.
C
OK
PRemove VSV for EGR. (See page EC±13).
Measure resistance between terminals of VSV for EGR.
Resistance: 38.5 ± 44.5
at 20  C (68  F)
Replace VSV for EGR.
3Check for open and short in harness and connector between EFI main relay and \
VSV for EGR,
VSV for EGR and engine (& ECT) ECU. (See page IN±27)
Repair or replace harness or connector.
Check and replace engine (& ECT) ECU.
TR±108±
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