Lexus SC300 / Lexus SC400. Manual — part 894
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
).
Check for open in harness and connector
between battery and ECU.
Replace cold start injector.
WIRING DIAGRAM
–
ENGINE TROUBLESHOOTING
Circuit Inspection
TR–137
NG
OK
OK
NG
INSPECTION PROCEDURE
1
Check voltage between terminal STJ of engine & ECT ECU connector and body ground.
C
OK
Hint
P
Connect to the Check Harness A.
(See page
Disconnect start injector time switch connector.
Disconnect engine & ECT ECU connector.
Measure voltage between terminal STJ of engine &
ECT ECU connector and body ground when ignition
switch is turned to STA.
10 – 14 V
Go to step 3.
2
Check resistance of cold start injector.
C
OK
Hint
P
Remove cold start injector (See page
Measure resistance between terminals of cold start in-
jector.
Resistance:
2 – 4
at 20
C (68
F)
Replace cold start injector.
Check and repair harness and connector between
engine & ECT ECU and cold start injector, cold
start injector and battery.
TR–138
–
ENGINE TROUBLESHOOTING
Circuit Inspection
OK
NG
OK
NG
OK
NG
3
Check start injector time switch.
C
OK
P
Remove start injector time switch (See page FI–88).
Measure resistance between terminals shown below.
Replace start injector time switch.
4
Check harness and connector between cold start injector and start injector time switch (See
page
).
Repair or replace harness or connector.
5
Check fuel injection of cold start injector.
C
OK
P
Remove cold start injector (See page
(2) Check fuel injection of cold start injector
(See page
).
(2) Check fuel leakage of cold start injector
(See page
).
(2) Fuel is injected normally.
(2) Fuel leakage is less than one drop per minute.
Notice:
Perform this check within the shortest possible
time.
Repair or replace cold start injector.
Proceed to next circuit inspection shown on ma-
trix chart (See page
).
–
ENGINE TROUBLESHOOTING
Circuit Inspection
TR–139
ISC Valve Circuit
CIRCUIT DESCRIPTION
The ISC valve is provided on the intake air chamber and in-
take air bypassing the throttle valve is directed to the ISC
valve through a hose.
A step motor is built into the ISC valve. It consists of four
coils, the magnetic rotor, valve shaft and valve. When cur-
rent flows to the coils due to signals from the ECU, the rotor
turns and moves the valve shaft forward or backward,
changing the clearance between the valve and the valve
seat.
In this way the intake air volume bypassing the throttle valve
is regulated, controlling the engine speed.
There are 125 possible positions to which the valve can be
opened.
DIAGNOSTIC CHART
DIAGNOSTIC CHART
Check operation for ISC valve.
Replace ISC valve.
Repair or replace harness or
connector.
Proceed to next circuit inspection shown on
matrix chart (See page
).
Check harness and connector between EFI
main relay, ISC valve and ECU.
TR–140
–
ENGINE TROUBLESHOOTING
Circuit Inspection
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