Lexus SC300 / Lexus SC400. Manual — part 889

OK

NG

Type I

NG

Type II

NG

OK

OK

NG

INSPECTION PROCEDURE

1

Check output condition of diag. code 51.

C

P

(2) Connect terminals TE2 and E1 of TDCL.

(2) Turn ignition switch on.

(2) Crank the engine.

(2) Connect terminal TE1 and E1 of TDCL.

Check if diagnostic code “51” is output when then shift
level is in the P and D shift positions.

Result:

Go to step 2.

Go to step 3.

Proceed to next circuit inspection shown on ma-

trix chart (See page

TR–35

).

2

Check for open in harness and connector between engine & ECT ECU and neutral start switch

(See page

IN–27

).

Check and replace engine & ECT ECU.

Repair or replace harness or connector.

3

Check neutral start switch (See page

AT–100

).

Replace neutral start switch.

Check and replace engine & ECT ECU.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–123

ECU Power Source Circuit

CIRCUIT DESCRIPTION

When the ignition switch is turned on, battery voltage
is applied to the terminal IG SW of the ECU, and the
main relay control circuit in the ECU sends a signal to
the terminal M–REL of the ECU, switching on the
main relay. This signal causes current to flow to the
coil, closing the contacts of the main relay and supply-
ing power to the terminals +B and +B1 of the ECU.
If the ignition switch is turned off, the ECU continues
to switch on the main relay for a maximum of 2 se-
conds for the initial setting of the ISC valve.

DIAGNOSTIC CHART

DIAGNOSTIC CHART

See next page for the DIAGNOSTIC CHART.

WIRING DIAGRAM

TR–124

–

ENGINE TROUBLESHOOTING

Circuit Inspection

DIAGNOSTIC CHART

DIAGNOSTIC CHART

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

Check voltage of terminal M–REL.

Check for open in harness and connector
between battery and ECU.

Check and replace ECU.

Replace ignition switch.

Repair or replace harness or
connector.

Repair or replace harness or
connector.

Check for open and short in harness and
connector between terminal M REL and body
ground.

Replace EFT main relay.

Check voltage of terminal IGSW.

Check IGN fuse.

Check continuity between terminals E1 and
body ground.

Check voltage of ECU power source.

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

TR–35

).

Check ignition switch.

Check EFT fuse.

Check EFT main relay.

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

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

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–125

NG

OK

OK

NG

NG

OK

INSPECTION PROCEDURE

1

Check voltage between terminals + B, + B1 and E1 of engine & ECT ECU connector.

C

OK

P

(2) Connect the Check Harness A.

(See page

TR–30

)

(2) Turn ignition switch on.

Measure voltage between terminals + B, + B1 and E1
of engine & ECT ECU connector.

Voltage:

10 – 14 V

Proceed to next circuit inspection shown on matrix chart

2

Check for open in harness and connector between terminals E1 of engine & ECT ECU and body
ground (See page

IN–27

).

Repair or replace harness or connector.

3

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

C

OK

P

Turn ignition switch on.

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

Voltage:

10 – 14 V

Go to step 6.

TR–126

–

ENGINE TROUBLESHOOTING

Circuit Inspection