Lexus SC300 / Lexus SC400. Manual - part 172

WIRING DIAGRAM

Ignition Switch Circuit

CIRCUIT DESCRIPTION

This circuit sends an ignition switch ON or OFF signal to the ECU.

DIAGNOSTIC CHART

DIAGNOSTIC CHART

Check ECU–IG fuse.

NG

Check for short in all the harness
and components connected to
ECU–IG fuse.

Check voltage between terminal IG of
ECU connector and body ground.

OK

OK

NG

Proceed to next circuit inspection
shown on matrix chart 

(See page 

BE–276

).

Check and repair harness or connector 

between ECU and battery (See page 

IN–27

).

BE–302

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Driver’s Seat)

OK

NG

NG

OK

INSPECTION PROCEDURE

1

Check ECU – IG fuse.

Check for short in all the harness and components con-
nected to ECU–IG fuse.

2

Check voltage between terminal IF of ECU connector and body ground.

C

P

Remove ECU with connectors still connected.

Measure voltage between terminal IG of ECU connector
and body ground when ignition switch is on and off.

Ignition switch

Voltage

ON

OFF

10 – 14 V

Below 1 V

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

BE–276

).

Check and repair harness or connector between

ECU and battery (See page 

IN–27

).

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Driver’s Seat)

BE–303

WIRING DIAGRAM

Check voltage between each termi-
nal and a SGND of ECU connector.

OK

NG

NG

NG

OK

OK

Check power seat switch.

Replace power seat switch.

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

BE–276

).

Check harness and connectors between
ECU and power seat switch (See page

IN–27

).

Repair or replace harness
or connector.

Check and replace ECU.

Power Seat Switch Circuit

CIRCUIT DESCRIPTION

When the power seat switch is operated, a signal is sent from the power seat switch to the ECU and the ECU
sends a signal to the motor to make it operate (except for the lumbar support).
Even if a malfunction should occur with the position sensor and return operation is prohibited, manual operation
will occur as normal.

DIAGNOSTIC CHART

DIAGNOSTIC CHART

BE–304

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Driver’s Seat)

NG

OK

OK

NG

OK

NG

INSPECTION PROCEDURE

1

Check voltage between each terminal and SGND ECU connector.

C

OK

P

Remove ECU with connectors still connected.

Measure voltage between each terminal of the manual
switch and SGND of ECU connector.

At each terminal

With SW ON

Below 1 V

With SW OFF

10 – 14 V

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

BE–276

).

2

Check power seat switch.

C

P

Disconnect power seat switch connector.

Check continuity of each terminal.

Replace power seat switch.

3

Check for open and short in harness and connectors between ECU and power seat switch (See

page 

IN–27

).

Repair or replace harness or connector.

Check and replace ECU.

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Driver’s Seat)

BE–305