Lexus SC300 / Lexus SC400. Service manual - part 840

WIRING DIAGRAM

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–133

NG

OK

OK

NG

INSPECTION PROCEDURE

1

Check 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.

2

Check ignition relay.

C

OK

Hint

P

Remove 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

–

ENGINE TROUBLESHOOTING

Circuit Inspection

OK

NG

OK

NG

OK

NG

3

Check for open in harness and connector between terminal E01, E02 of engine & ECT ECU con-
nector and body ground (See page 

IN–27

).

Repair or replace harness or connector.

4

Check 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.

5

Check 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

).

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–135

Cold Start Injector Circuit

CIRCUIT DESCRIPTION

The cold start injector is used to maintain the engine startability when it is cold. The injection volume, i,e, the
length of time the injector is energized, is controlled by the ECU and the cold start injector time switch.
During a cold start, when the starter turns the contacts in the cold start injector time switch close. Thus current
flows to the cold start injector coil, injecting fuel. At the same time, a bimetal in the heat coil is energized and
heats up. This soon causes the contacts to open, cutting off the current flow to the injector coil and stopping
fuel injection.
The injection duration of the cold start injector is determined by the coolant temperature and the length of time
current flows to the heat coil. When the engine is warm, the contacts are opened by the bimetal and the cold
start injector does not operate.
When the engine is hard to start and the starter is operated continuously, heat coil (2) heats up the bimetal keep-
ing the contacts open to prevent spark plugs from becoming fouled, which is caused by the cold start injector
operation when the open contacts close again.
When the engine is started at a coolant temperature of 22

°

C (72

°

F) or lower, the cold start injector operation

time is controlled by the cold start injector time switch.
When the coolant temperature is in the normal temperature range 22

°

C (72

°

F) or higher, the contacts of the cold

start injector time switch are open and the time switch is off, instead, the ECU controls the operating time of the
cold start injector.
In this way, the CO and HC levels can be reduced while the engine is being started and the engine startability
is maintained. Control by the ECU ends when the coolant temperature reaches 60

°

C (140

°

F).

TR–136

–

ENGINE TROUBLESHOOTING

Circuit Inspection