Lexus SC300 / Lexus SC400. Manual - part 841

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

–

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 

TR–30

)

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 

FI–27

).

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 

IN–27

).

Repair or replace harness or connector.

5

Check fuel injection of cold start injector.

C

OK

P

Remove cold start injector (See page 

FI–27

).

(2) Check fuel injection of cold start injector

(See page 

FI–33

).

(2) Check fuel leakage of cold start injector

(See page 

FI–34

).

(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 

TR–35

).

–

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 

TR–35

).

Check harness and connector between EFI
main relay, ISC valve and ECU.

TR–140

–

ENGINE TROUBLESHOOTING

Circuit Inspection