Lexus SC300 / Lexus SC400. Manual — part 922

CIRCUIT DESCRIPTION (Cont’d)

DIAGNOSIS CODE DETECTION DRIVING PATTERN

Purpose of the driving pattern.
(a) To simulate diag. code detecting condition after diag. code is recorded.
(b) To check that the malfunction is corrected when the repair is completed confirming that diag. code is

no longer detected.

Disconnect the EFI fuse (15 A) for 10 sec. or more. with IG switch OFF.
Initiate test mode (Connect terminal TE2 and E1 of check connector or TDCL with IG
switch OFF).

Start engine and warm up with all ACC switch OFF.

After engine is warmed up, let it idle for 5 min.
(After the engine is started, do not depress the accelerator pedal.)

If the malfunction is not detected during idling, perform racing without any load at
approx. 2,000 rpm for 60 sec.

HINT: If a malfunction exists, the ”CHECK” engine warning light will light up during the 5

min. idling period or within 60 sec. of starting racing.

NOTICE: If the conditions in this test are not strictly followed, detection of the

malfunction will not be possible.

Malfunction: Open or Short in Injector circuit, Injector Leak or Blockage

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–71

DIAGNOSTIC CHART

Check voltage of terminal VF.

Repair or replace harness or
connector.

Repair or replace.

Repair or replace.

Replace main oxygen sensor.

Repair or replace.

Repair or replace.

Replace main oxygen sensor.

Check voltage of terminal OX.

Check for open and short in harness and
connector.

Check each item found to be a possible
cause of problem.

Check compression.

Does malfunction disappear when a good
main oxygen sensor is installed?

Check and replace ECU.

Check each item found to be a possible
cause of problem.

Check compression.

Does malfunction disappear when a good
main oxygen sensor is instaled?

Check and replace ECU.

NG T

ype

II

NG Type

I

WIRING DIAGRAM

Refer to page

TR–62

for the WIRING DIAGRAM.

TR–72

–

ENGINE TROUBLESHOOTING

Circuit Inspection

NG

Type

I

NG

Type

II

NG

OK

INSPECTION PROCEDURE

1

Check voltage between terminals VF1, VF2 and E1 of check connector.

C

P

Cau-

tion

1.

Warm up engine at normal operating temperature

2.

Connect terminals TE1 and E1 of check connector.

3.

Connect positive prove to terminal VF1, VF2 and
negative prove to terminal E1 of check connector.

1.

Warm up the oxygen sensor by running engine at
2,500 rpm for about 2 minutes.

2.

Then, maintaining engine at 2,500 rpm, count how
many times needle of voltmeter fluctuates between
0 and 5 V.

Go to step

.

2

Check voltage between terminals OX1, OX2 and E1 of check connector.

C

OK

Hint

P

Warm up engine at normal operating temperature.

Measure voltage between terminals OX1, OX2 and E1
of check connector when engine is suddenly raced to
full throttle.

The voltage should be 0.5 V or higher at least once.

Perform inspection within 1 second.

Go to step

.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–73

OK

NG

OK

NG

OK

NG

NG

YES

3

Check for open and short in harness and connector between engine (& ECT) ECU and main

oxygen sensor, engine (& ECT) ECU and check connector (See page

IN–27

).

Repair or replace harness or connector.

4

Check each item found to be a possible cause of problem.

Check each circuit found to be a possible cause of trouble according to the results of the check in

or

. The numbers in the table below show the order in which the checks should be performed.

Main oxygen sensor

signal from either side

continues at 0 V.

Main oxygen sensor

signals from both sides

continue at 0 V.

Possible Cause

See page

1

Faulty sensor installation.

–

3

Injector circuit

TR–128

2

3

Misfire

IG–6

4

Valve timing

EM–22

1

Air leakage

FI–7

2

Fuel system

TR–110

6

Characteristics deviation
in air flow meter.

TR–82

4

Characteristics deviation
in water temp. sensor.

TR–64

5

Characteristics deviation
in intake air temp. sensor.

TR–68

Repair or replace.

5

Check compression (See page

EM–22

).

Repair or replace.

6

Does malfunction disappear when a good main oxygen sensor is installed?

Replace main oxygen sensor.

Check and replace engine (& ECT) ECU.

TR–74

–

ENGINE TROUBLESHOOTING

Circuit Inspection