Lexus SC300 / Lexus SC400. Service manual - part 171

Check stop light operation.

NG

OK

OK

NG

Check stop light circuit

(See page 

BE–64

).

Proceed to next circuit inspection
shown on matrix chart 

(See page 

BE–276

).

Check voltage between terminals STOP
of ECU connector and body ground.

Check and repair harness and connec-
tor between ECU and stop light switch.

WIRING DIAGRAM

Stop Light Circuit

CIRCUIT DESCRIPTION

The stop light switch sends a brake ON of Off signal to the ECU.  When the ECU receives a brake ON signal
it prohibits return of the seat.

DIAGNOSTIC CHART

DIAGNOSTIC CHART

BE–298

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Driver’s Seat)

OK

NG

NG

OK

INSPECTION PROCEDURE

1

Check stop light operation.

Check that the stop light comes on when the brake pedal is depressed, and turns off when the pedal
is released.

C

Check stop light circuit. (See page 

BE–64

).

2

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

C

OK

Hint

P

Remove ECU with connectors still connected.

Measure voltage between terminal STOP of ECU and
body ground when the brake pedal is depressed and re-
leased.

Brake pedal

Voltage

Depressed

10 – 14 V

Released

Below 1 V

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

BE–276

).

Check and repair harness and connector between
ECU and stop light switch.

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Driver’s Seat)

BE–299

WIRING DIAGRAM

Check shift position indicator.

NG

OK

OK

NG

Check shift position indicator
circuit (See page BE– 141).

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

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

BE–276

).

Check and repair harness and connector
between ECU and connector.

Neutral Start Switch Circuit

CIRCUIT DESCRIPTION

The neutral start switch detects when the shift position is in P range and sends a signal to the ECU.  
When the return switch is turned ON with the IG SW ON and the shift in P range, the ECU performs 
return operation.

DIAGNOSTIC CHART

DIAGNOSTIC CHART

BE–300

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Driver’s Seat)

OK

NG

NG

OK

INSPECTION PROCEDURE

1

Check the shift position indicator.

Check that P lights up on the shift indicator when P range is shifted into, and that P is OFF when
shifting into another range.

C

Check shift position indicator circuit (See page BE–141).

2

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

C

OK

P

Remove ECU with connectors still connected.

(1) Turn ignition switch ON.

(2) Measure voltage between terminal P of ECU con-

nector and body ground when the shift lever is posi-
tioned to the following ranges.

Shift range

P

10

Other than P

Voltage

10 – 14 V

Below 1 V

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

BE–276

).

Check and repair harness and connector between
ECU and connector.

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Driver’s Seat)

BE–301