Lexus SC300 / Lexus SC400. Manual - part 685

OK

NG

OK

NG

6

Check voltage between terminal M–REL of engine & ECT ECU connector and body ground.

C

OK

P

Turn ignition switch on.

Measure voltage between terminal M–REL of engine &
ECT ECU connection and body ground.

Voltage:

10 – 14 V

Check and replace engine & ECT ECU.

7

Check EFI

C

OK

P

Remove EFI fuse R/B No.2.

Check continuity of EFI fuse.

Continuity

Rep

TR–128

–

ENGINE TROUBLESHOOTING

Circuit Inspection

OK

NG

OK

NG

8

Check EFI main relay.

C

OK

P

C

OK

Remove EFI main relay.

Check continuity between terminals of EFI main relay
shown below.

(2) Apply battery voltage between terminals 1 and 3.

(2) Check continuity between terminals 2 and 4.

Replace EFI main relay.

9

Check for open and short in harness and connector between terminal M–REL of engine & ECT
ECU and body ground (See page 

IN–27

).

Repair or replace harness or connector.

Check and repair harness or connector between
EFI fuse and battery.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–129

Back Up Power Source Circuit

CIRCUIT DESCRIPTION

Battery voltage is supplied to terminal BATT of the ECU even when the ignition switch is off for use by
the diagnostic code memory and air–fuel ratio adaptive control value memory, etc.

DIAGNOSTIC CHART

DIAGNOSTIC CHART

Check for short in all the harness and
components connected to EFI fuse.

Check EFI fuse.

Check of terminal BATT.

Proceed to next circuit inspection shown on
matrix chart (See page 

TR–35

).

Check operation for the back up.

Check and replace ECU.

Check and repair harness or connector
 between battery, EFI fuse and ECU.

WIRING DIAGRAM

TR–130

–

ENGINE TROUBLESHOOTING

Circuit Inspection

OK

NG

OK

NG

YES

NO

INSPECTION PROCEDURE

1

Check EFI fuse.

C

OK

P

Remove EFI fuse from R/B No.2.

Check continuity of EFI fuse.

Continuity

Check for short in all the harness and components con-
nected to EFI fuse (See attached wiring diagram).

2

Check voltage between terminal BATT of engine & ECT ECU connector and body ground.

C

OK

P

Connect the Check Harness A.
(See page 

TR–30

).

Measure voltage between terminal BATT of engine &
ECT ECU connector and body ground.

Voltage:

10 – 14 V

Check and repair harness or connector between engine
& ECT ECU and EFI fuse, EFI fuse and battery.

3

Are the diagnostic codes still in the memory when the ignition switch is turned OFF?

Check and replace engine & ECT ECU.

Proceed to next circuit inspection shown on ma-
trix chart (See page 

TR–35

).

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–131