Lexus SC300 / Lexus SC400. Manual - part 179

NG

OK

1

Position sensor check (Cont’d).

OK

Hint

(4) Operate the power seat manual switch and check

the change in the voltage when the seat is moving.

(5) The changes in the output voltage when the input

signal is normal and when it is abnormal are shown
in the illustrations.  Compare the results with those
from (4) and diagnose the condition of each circuit.

  The OK and NG codes continue to be output while the

manual switch is ON.

  When the seat reaches the limit of movement, e.g. 

when the headrest reaches the highest or lowest 
position, the voltage changes from the OK code to 
the NG code.

After operating any of the system functions with no
problem and confirming the OK code and NG code by
comparing the amount of wavering of the voltmeter
needle, inspect the function with a problem.

The amount of wavering of the voltmeter needle 
depends on the meter.

Output

OK

NG

OK Code

NG Code

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

BE–318

).

Go to step [2].

BE–332

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Passenger’s Seat)

OK

NG

OK

NG

2

Check position sensor.

C

OK

Hint

P

Disconnect the connector of the sensor and the connec-
tor of the motor leading to the sensor.

(1) Connect the positive 

 lead to terminal 3 of sensor

and negative 



 lead to terminal 2.

(2) Measure voltage between terminal 1 of sensor and

body ground when battery voltage is applied be-
tween terminals 1 and 2 of motor connector.

When the battery voltage is applied to the motor con-
nector terminals, 

 and 



 are interchangeable.

Condition

Voltage

Motor stopped

0 V or battery
voltage ac-
cording to
stop position

Motor Turning

(Check several times
with the motor in a differ-
ent position each time.)

half of battery
voltage

Replace position sensor.

3

Check for open and short in harness and connectors between ECU and position sensor (See

page 

IN–27

).

Repair or replace harness or connectors.

Check and replace ECU.

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Passenger’s Seat)

BE–333

Slide Switch Circuit

CIRCUIT DESCRIPTION

When the power seat control switch is operated, a signal is sent to the ECU and the ECU applies the power
source to the slide motor.

DIAGNOSTIC CHART

DIAGNOSTIC CHART

Check voltage between terminals SDLF,
SLDR of ECU connector and body ground.

OK

NG

OK

OK

OK

OK

NG

NG

NG

NG

NG

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

BE–319

).

Check DOOR fuse.

Check for short in all the harness
and components connected to the
DOOR fuse (See attached wiring
diagram). *

1

Check voltage between terminals B1 and E1
of power seat control switch connector.

Check continuity between terminal E1 of pow-
er seat switch connector and body ground.

Repair or replace harness and
connector.

Check harness and connector between
battery and ECU.

Check power seat control switch.

Replace power seat control
switch.

Check harness and connector between
power seat control switch and ECU.

Repair or replace harness and
connector.

Check and replace ECU.

*

1

The power source is supplied to the actuator
(Slide motor) through the passenger’s seat
ECU accordingly, if a short circuit of the W/H
or actuator occurs in the actuator circuit, the
DOOR fusible link may become open, so
also inspect the actuator. 

(Slide motor circuit on page 

BE–328

).

BE–334

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Passenger’s Seat)

WIRING DIAGRAM

NG

OK

*1  The power source is supplied to the actuator

(Slide motor) through the passenger’s seat
ECU accordingly, if a short circuit of the W/H
or actuator occurs in the actuator circuit, the
DOOR fusible link may become OPEN, so
also inspect the actuator.  
(Slide motor circuit on page 

BE–328

).

OK

NG

INSPECTION PROCEDURE

1

Check voltage between terminals SLDF, SLDR, of ECU connector and body ground.

C

OK

P

Remove ECU with connector still connected.

Measure voltage between SLDF, SLDR terminal and
body ground, when slide switch is operated.

Switch condition

Voltage (V)

SLDF

SLDR

Forward

Back

10 – 14 V

Below 1 V

Below 1 V

10 – 14 V

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

BE–319

).

2

Check DOOR fuse.

Check for short in all the harness and components con-
nected to the DOOR fuse and repair them (See attached
wiring diagram). *1

Go to step [3].

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Passenger’s Seat)

BE–335