check engine LEXUS SC400 1991 Service Repair Manual

NGOK
OKNG
NGOK
INSPECTION PROCEDURE
1Check voltage between terminals + B, + B1 and E1 of engine & ECT ECU connecto\
r.
C
OK
P(2) Connect the Check Harness A.(See page TR±30)
(2) Turn ignition switch on.
Measure voltage between terminals + B, + B1 and E1
of engine & ECT ECU connector.
Voltage: 10 ± 14 V
Proceed to next circuit inspection shown on matrix chart
2Check for open in harness and connector between terminals E1 of engine &\
ECT ECU and body
ground (See page IN±27).
Repair or replace harness or connector.
3Check voltage between terminal IG SW of engine & ECT ECU connector and b\
ody ground.
C
OK
PTurn ignition switch on.
Measure voltage between terminal IG SW of engine &
ECT ECU connector and body ground.
Voltage: 10 ± 14 V
Go to step 6.
TR±126
±
ENGINE TROUBLESHOOTING Circuit Inspection
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OKNG
OKNG
4Check IGN Fuse.
C
OK
PRemove IGN fuse from J/B No.1.
Check continuity of IGN fuse.
Continuity.
Check for short in all the harness and components con-
nected to IGN fuse (See attached wiring diagram).
5Check ignition switch.
C
OK
PRemove under cover and finish panel.
Check continuity between terminals.
continuity
Replace ignition switch.
Check and repair harness and connector between
battery and ignition switch, ignition switch and en-
gine & ECT ECU.
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ENGINE TROUBLESHOOTING Circuit InspectionTR±127
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OKNG
OKNG
6Check voltage between terminal M±REL of engine & ECT ECU connector and bod\
y ground.
C
OK
PTurn ignition switch on.
Measure voltage between terminal M±REL of engine &
ECT ECU connection and body ground.
Voltage: 10 ± 14 V
Check and replace engine & ECT ECU.
7Check EFI
C
OK
PRemove EFI fuse R/B No.2.
Check continuity of EFI fuse.
Continuity
Rep
TR±128
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ENGINE TROUBLESHOOTING Circuit Inspection
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OKNG
OKNG
8Check EFI main relay.
C
OK
P
C
OK
Remove EFI main relay.
Check continuity between terminals of EFI main relay
shown below.
(2) Apply battery voltage between terminals 1 and 3.
(2) Check continuity between terminals 2 and 4.
Replace EFI main relay.
9Check for open and short in harness and connector between terminal M±REL o\
f engine & ECT
ECU and body ground (See page IN±27).
Repair or replace harness or connector.
Check and repair harness or connector between
EFI fuse and battery.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±129
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Back Up Power Source Circuit
CIRCUIT DESCRIPTION
Battery voltage is supplied to terminal BATT of the ECU even when the ignition switch is off for use by
the diagnostic code memory and air±fuel ratio adaptive control value mem\
ory, etc.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
Check for short in all the harness and
components connected to EFI fuse.Check EFI fuse.
Check of terminal BATT.
Proceed to next circuit inspection shown on
matrix chart (See page TR±35).
Check operation for the back up.Check and replace ECU.
Check and repair harness or connector
between battery, EFI fuse and ECU.
WIRING DIAGRAM
TR±130±
ENGINE TROUBLESHOOTING Circuit Inspection
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OKNG
OKNG
YESNO
INSPECTION PROCEDURE
1Check EFI fuse.
C
OK
PRemove EFI fuse from R/B No.2.
Check continuity of EFI fuse.
Continuity
Check for short in all the harness and components con-
nected to EFI fuse (See attached wiring diagram).
2Check voltage between terminal BATT of engine & ECT ECU connector and body ground.
C
OK
PConnect the Check Harness A.
(See page TR±30).
Measure voltage between terminal BATT of engine &
ECT ECU connector and body ground.
Voltage: 10 ± 14 V
Check and repair harness or connector between engine
& ECT ECU and EFI fuse, EFI fuse and battery.
3Are the diagnostic codes still in the memory when the ignition switch is\
turned OFF?
Check and replace engine & ECT ECU.
Proceed to next circuit inspection shown on ma-
trix chart (See page TR±35).
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±131
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Injector Circuit
CIRCUIT DESCRIPTION
The injectors are provided to the intake manifold. They inject fuel into th\
e cylinders based on the signals from
the engine & ECT ECU.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
Replace ignition relay.
Check voltage between terminals #10 ~ 40 of
engine & ECT ECU and body ground.
Check ignition relay.
Check continuity between terminal E01, E02
and body ground.Repair or replace harness or
connector.
Repair or replace harness or
connector.
Replace injector.
Check for open in harness and connector
between ignition relay and ECU.
Check operation for injectors.
Proceed to next circuit inspection shown on
matrix chart (See page TR±35).
Check and repair harness and connector
between ignition relay and battery.
TR±132±
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NGOK
OKNG
INSPECTION PROCEDURE
1Check voltage between terminals #20 ~ 40 of engine & ECT ECU and body ground.\
C
OK
P(2) Connect the Check Harness A.(See page TR±30)
(2) Turn ignition switch on.
Measure voltage between terminals #10 ~ 40 of engine
& ECT ECU and body ground.
Voltage: 10 ± 14 V
Go to step 3.
2Check ignition relay.
C
OK
Hint
PRemove ignition relay from R/B No.2.
Check continuity between terminals of ignition relay
shown below.
(2) Apply battery voltage between terminals of ignition relay shown below.
(2) Check continuity between terminals 1 and 2.
Replace ignition relay.
TR±134
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ENGINE TROUBLESHOOTING Circuit Inspection
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OKNG
OKNG
OKNG
3Check for open in harness and connector between terminal E01, E02 of eng\
ine & ECT ECU con-
nector and body ground (See page IN±27).
Repair or replace harness or connector.
4Check for open in harness and connector between ignition relay and injector, injector and en-
gine & ECT ECU (See page IN±27).
Repair or replace harness or connector.
5Check injectors.
C
OK
P
OK
C
Disconnect injector connector (See page FI±50).
Measure resistance of injector.
Resistance: 13.4 ± 14.2
at 20 C (68 F)
Check injection volume of injector (See page FI±52).

Injection volume
55±70 cc/15 sec. (3.4±4.3 cu in.)
Difference between each injector:
Less than 10 cc (0.6 cu in.)

Leakage
Fuel drop: Once drop or less per minute.
Replace injector.
Proceed to next circuit inspection shown on ma-
trix chart (See page TR±35).
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ENGINE TROUBLESHOOTING Circuit InspectionTR±135
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DIAGNOSTIC CHART
DIAGNOSTIC
CHART
Check voltage of cold start injector power
source.
Check cold start injector.
Check start injector time switch.Replace start injector time switch.
Repair or replace harness or
connector.
Replace cold start injector.
Check for open and short in harness and
connector between cold start injector and
start injector time switch.
Check fuel injection of cold start injector.
Proceed to next circuit inspection shown on
matrix chart (See page TR±35).
Check for open in harness and connector
between battery and ECU.
Replace cold start injector.
WIRING DIAGRAM
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ENGINE TROUBLESHOOTING Circuit InspectionTR±137
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