Lexus SC300 / Lexus SC400. Manual - part 926

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 with IG switch
OFF).



Start the engine and warm up with all ACC switch OFF.



After the engine is warmed up, let it drive at 50  55 mph (80  88 km/h) for 10 min. or
more.



After driving, stop at a safe place and perform idling for 2 min. or less.



After performing the idling in , perform acceleration to 60 mph (96 km/h) with the
throttle valve fully open.

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

step 



.

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

malfunction will not be possible.

Malfunction: Open or Short in Sub–Oxygen Sensor

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–77

DIAGNOSTIC CHART

HINT: When other codes are output in addition to 27 at the same time, check the circuits for other

codes first.

WIRING DIAGRAM

Check voltage between terminal HT.

Check resistance of sub–oxygen sensor
heater.

Check for open and short in harness and
connector between EFI main relay and ECU.

Check and replace ECU.

Check operation of sub–oxygen sensor
heater.

Check and replace ECU.

Replace sub–oxygen sensor.

Repair or replace harness or
connector.

Replace sub–oxygen sensor.*

*: In this case, oxygen sensor can be

deteriorated.

TR–78

–

ENGINE TROUBLESHOOTING

Circuit Inspection

NG

OK

OK

NG

INSPECTION PROCEDURE

1

Check voltage between terminal HT of engine (&ECT) ECU connector and body ground.

C

OK

P

1.

Connect the Check Harness A. (See page 

TR–34

).

2.

Turn ignition switch on.

Measure voltage between terminal HT of engine (&
ECT) ECU connector and body ground.

Voltage:

10 – 14 V

Go to step 

.

2

Check sub–oxygen sensor heater.

C

OK

P

Disconnect sub–oxygen sensor connector.

(See page 

FI–78

).

Measure resistance between terminals 1 and 2 of
sub–oxygen sensor connector.

Resistance:

5.1 – 6.3 

 20

°

C (68

°

F)

Replace sub–oxygen sensor.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–79

OK

NG

NG

OK

3

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

ECU (See page 

IN–27

).

Repair or replace harness or connector.

Check and replace engine (& ECT) ECU.

4

Check voltage between terminal HT of engine (& ECT) ECU connector and body ground.

C

OK

P

Warm up engine to normal operating temperature.

Measure voltage between terminal HT of engine (&
ECT) ECU connector and body ground, when engine is
idling and racing at 3,500 rpm.

Replace sub–oxygen sensor.*

*: In this case, oxygen sensor can be deteriorated.

Check and replace engine (& ECT) ECU.

TR–80

–

ENGINE TROUBLESHOOTING

Circuit Inspection