Lexus SC300 / Lexus SC400. Service manual - part 181

Limit Switch Circuit

CIRCUIT DESCRIPTION

Slide neutral limit switch:  this switch is on when passenger’s seat is slided approx. 120 or more from the most

back position.

Reclining from limit switch:  this switch is on, when passenger’s seat back is reclining forward.
Reclining rear limit switch:  when passenger’s seat back returns to upright, this is on.

DIAGNOSTIC CHART

DIAGNOSTIC CHART

For each symptom, inspect the circuit indicated in the table.

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Symptom

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Inspection circuit

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•

Only return operation is not functioning.

•

Seat returns to rear most position during return operation.

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Slide neutral limit switch.

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•

Walk–in function and return function do not operate.
(However, they operate when using the manual switch).

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Reclining front limit switch.
Reclining rear limit switch.

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•

Only walk–in operation is not functioning.

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Reclining front limit switch.

Check limit switch.

Check and replace ECU.

Check harness and connector between ECU
and limit switches, limit switches and SGND.

Check continuity between terminals SGND 
of ECU connector and body ground.

Check voltage between terminals SLSW,
RFSW, RRSW and SGND of ECU connector.

Proceed to next circuit inspection
shown on matrix chart 

(See page 

BE–319

).

Repair or replace harness
connector.

Replace the limit switch.

Repair or replace harness or
connector.

OK

NG

NG

NG

NG

OK

OK

OK

BE–340

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Passenger’s Seat)

NG

OK

OK

NG

INSPECTION PROCEDURE

1

Check voltage between terminals SLSW, RFSW, RRSW and SGND of ECU connector.

C

OK

P

Remove ECU with connector still connected.

Measure voltage between each terminal and SGND of
ECU connector.

When each limit switch is on and off.

Switch condition

Condition

Voltage

Slide neutral
limit switch

Reclining front
limit switch

Reclining rear
limit switch

ON

OFF

ON

OFF

ON

OFF

Seat is forward of the
neutral position.

Seat is to the rear of
the neutral position.

Seat back is fully reclined.

Others

Seat back is in the upright
position

Others

Below 1 V

10 – 14 V

Below 1 V

Below 1 V

10 – 14 V

10 – 14 V

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

BE–319

).

2

Check continuity between terminal SGND of ECU connector and body ground.

C

OK

P

Remove ECU with connector still connected.

Measure resistance between SGND of ECU connector
and body ground.

Resistance:

1 

 or less

Repair or replace harness or connector.

Go to step [3].

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Passenger’s Seat)

BE–341

OK

NG

OK

NG

WIRING DIAGRAM

3

Check each limit switch.

C

OK

P

Disconnect limit switch connector.

Check continuity of each terminal of limit switch.

Switch condition

Condition

Voltage

Slide neutral
limit switch

Reclining front
limit switch

Reclining rear
limit switch

ON

OFF

ON

OFF

ON

OFF

Seat is forward of the
neutral position.

Seat is to the rear of
the neutral position.

Seat back is fully reclined.

Others

Seat back is in the upright
position

Others

Continuity

Open

Continuity

Continuity

Open

Open

Replace the limit switch.

4

Check for open and short in harness and connector between ECU and limit switches, limit

switches and SGND (See page 

IN–27

).

Repair or replace harness or connector.

Check and replace ECU.

BE–342

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Passenger’s Seat)

WIRING DIAGRAM

Reclining Switch and Motor Circuit

CIRCUIT DESCRIPTION

When the power seat switch is turned to forward reclining, the seat back returns to upright.
When the switch is turned to rear reclining, the seat back reclines.

DIAGNOSTIC CHART

DIAGNOSTIC CHART

Check power seat switch.

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

NG

Check and repair harness and
connectors between battery and
power seat switch, power seat
switch and body ground.

NG

NG

OK

OK

OK

Check reclining motor.

Check and repair harness and connectors
between switch and motor.

Replace power seat switch.

Replace reclining motor.

BE–344

–

BODY ELECTRICAL SYSTEM

Power Seat Control System (Passenger’s Seat)