ignition switch LEXUS SC400 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±
ENGINE TROUBLESHOOTING Circuit Inspection
WhereEverybodyKnowsYourName

NGOK
OKNG
OKNG
INSPECTION PROCEDURE
HINT: If diagnostic codes º22º (water temperature sensor circuit), º2\
4º (intake air temperature sensor cir-cuit) and º41º (throttle position sensor circuit) are output simultan\
eously, E2 (sensor ground) may
be open.
1Check voltage between terminals THW and E2 of engine (&ECT) ECU connec\
tor.
C
OK
P1. Connect the Check Harness A. (See page TR±34)
2. Turn ignition switch on.
Measure voltage between terminals THW and E2 of en-
gine (& ECT) ECU connector.
Check for momentary interruption (See page TR±27).
2Check water temp. sensor.
C
OK
PDisconnect the water temp. sensor connector.
Measure resistance between terminals.
Resistance is within Acceptable Zone on chart.
Replace water temp. sensor.
3Check for open and short in harness and connector between engine (& ECT\
) ECU and water
temp. sensor (See page IN±27).
Repair or replace harness or connector.
Check and replace engine (& ECT) ECU.
TR±66±
ENGINE TROUBLESHOOTING Circuit Inspection
WhereEverybodyKnowsYourName

NGOK
OKNG
OKNG
INSPECTION PROCEDURE
HINT: If diagnostic codes º22º (water temperature sensor circuit), º\
24º (intake air temperature sensor circuit)and º41º (throttle position sensor circuit) are output simultane\
ously, E2 (sensor ground) may be open.
1Check voltage between terminals THW and E2 of engine & ECT ECU connector\
.
C
OK
P(2) Connect the Check Harness A.(See page TR±30)
(2) Turn ignition switch on.
Measure voltage between terminals THW and E2 and
engine & ECT ECU connector.
Check for momentary interruption
(See Page TR±23).
2Check water temp. sensor.
C
OK
PDisconnect the water temp. sensor connector.
(See page FI±99).
Measure resistance between terminals.
Resistance is within Acceptable Zone on chart.
Replace water temp. sensor.
3
Check for open and short in harness and connector between engine & ECT ECU and\
water temp.
sensor (See page IN±27).
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±70
WhereEverybodyKnowsYourName

NGOK
OKNG
OKNG
INSPECTION PROCEDURE
1Check voltage between terminals THA and E2 of engine & ECT ECU connector.
C
OK
P(2) Connect the Check Harness A.(See page TR±30)
(2) Turn ignition switch on.
Measure voltage between terminals THA and
E2 and engine & ECT ECU connector.
Check for momentary Intertuption
(See page TR±23).
2Check intake air temp. sensor.
C
OK
PDisconnect the air flow meter connector.
Measure resistance between terminals 1 and 2 of air
flow meter connector.
Resistance is within Acceptable Zone on chart.
Replace intake air temp. sensor (Replace air flow meter).
3
Check for open and short in harness and connector between engine & ECT ECU an\
d intake air
temp. sensor (See page IN±27).
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
TR±73±
ENGINE TROUBLESHOOTING Circuit Inspection
WhereEverybodyKnowsYourName

NGOK
OKNG
INSPECTION PROCEDURE
1Check voltage between terminal HT of engine (&ECT) ECU connector and body g\
round.
C
OK
P1. Connect the Check Harness A. (See page TR±34).
2. Turn ignition switch on.
Measure voltage between terminal HT of engine (&
ECT) ECU connector and body ground.
Voltage: 10 ± 14 V
Go to step
.
2Check sub±oxygen sensor heater.
C
OK
PDisconnect sub±oxygen sensor connector.
(See page FI±78).
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.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±79
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName

OKNG
NGOK
3Disconnect air flow meter connector and check voltage between terminals \
KS and E1 of engine
& ECT ECU.
C
OK
PDiconnect the air flow meter connector.
Turn ignition switch on.
Measure voltage between terminals KS and E1 of en-
gine & ECT ECU.
Voltage: 4 ± 6 V
Check and replace ECU.
4Diconnect air flow meter connector and check voltage between terminals VC and E1 \
of engine
& ECT ECU.
C
OK
PDiconnect the air flow meter connector.
Turn ignition switch on.
Measure voltage between terminals VC and E1 of en-
gine & ECT ECU.
Voltage: 4 ± 6 V
Replace air flow meter.
Check and replace engine & ECT ECU.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±91
WhereEverybodyKnowsYourName

NGOK
INSPECTION PROCEDURE
HINT:
wIf diag. code 41 is displayed, check throttle position sensor circuit. If \
diag. code 47 is displayed, check
sub±throttle position sensor circuit.
w If diag. codes º22º (water temperature sensor circuit), º24º\
(intake air temperature sensor circuit) and º41º
(throttle position sensor circuit) are output simultaneously, E2 (sensor ground) may be open.
#Check voltage between terminals VTA1, 2, IDL1, 2 and E2 of engine & ECT ECU connector.
C
OK
Hint
P(2) Connect the Check Harness A.
(See page TR±30).
(2) Turn ignition switch on.
(2) For sub±throttle position sensor, remove intake air duct and disconnect sub±throttle valve step motor
connector.
Measure voltage between terminals VTA1, 2, IDL1, 2
and E2 of engine & ECT ECU connector when the
(sub±) throttle valve is opened gradually from the closed
condition.
The voltage should increase steadily in proportion to the
throttle valve opening angle.
Check for Momentary interruption
(See page TR±23).
Go to step [2].
TR±96±
ENGINE TROUBLESHOOTING Circuit Inspection
WhereEverybodyKnowsYourName

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
±
ENGINE TROUBLESHOOTING Circuit Inspection
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName