LEXUS SC400 1991 Service Repair Manual

WIRING DIAGRAM
Position Sensor Circuit
CIRCUIT DESCRIPTION
The position sensor senses movement of the seat and send
pulse signals to the ECU. The position sensor sends pulses
to the ECU in proportion to the amount of seat movement, as
shown in the diagram on the left.
If a malfunction occurs in a position sensor and a sensor sig-
nal is not input to the ECU even when the motor operates, the
ECU prohibits return operation.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
Inspect the circuit which is malfunctioning.
Position sensor check.OK
NG
OK
OK NG
NG Proceed to next circuit inspection
shown on matrix chart (See page
BE±319
)
Replace position sensor.
Check position sensor.
Check harness and connectors between
ECU and position sensor (See page IN±27). Repair or replace harness or
connector.
Check and replace ECU.
BE±330±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)
WhereEverybodyKnowsYourName

INSPECTION PROCEDURE
1Position Sensor Check.
C
Hint
P(1) Remove the passenger's seat.
(2) Remove the bolts for seat rail and lift the seat cush-ion up a little.
Notice: If the seat cushion is lifted too high, the har-
ness will be pulled and the clamp may come loose.
(3) Remove the ECU with the connector attached from where it is installed to the underside of the seat
cushion.
Position sensor check
(1) Connect terminal CHK of the ECU to body ground to put the ECU into check mode.
(2) Measure voltage between terminal DOUT of ECU and body ground.
Use an analog type meter.
(3) Check that the ªreadyº code is output as shown in the illustration.
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)BE±331
WhereEverybodyKnowsYourName

NGOK
1Position sensor check (Cont'd).
OK
Hint
(4) Operate the power seat manual switch and checkthe 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.
OutputOK
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)
WhereEverybodyKnowsYourName

OKNG
OKNG
2Check position sensor.
C
OK
Hint
PDisconnect 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 posit\
ion 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
WhereEverybodyKnowsYourName

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 CHARTDIAGNOSTIC 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. *
1The 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)
WhereEverybodyKnowsYourName

WIRING DIAGRAM
NGOK
*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).
OKNG
INSPECTION PROCEDURE
1Check voltage between terminals SLDF, SLDR, of ECU connector and body ground.
C
OK
PRemove 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).
2Check 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
WhereEverybodyKnowsYourName

NGOK
OKNG
3Check voltage between terminals B1 and E1 of power seat switch connector.
C
OK
PRemove power seat switch with connector still con-
nected.
Measure voltage between terminal B1 and E1 of power
seat switch connector.
Voltage: 10 ± 14 V
Go to step 5.
4Check continuity between terminal E1 or power seat switch connector and \
body ground.
C
OK
PDisconnect power seat switch connector.
Check continuity of E1 terminal.
Resistance: 1
or less
Repair or replace harness or connector.
Check for open and short in harness and connec-
tor between ECU and battery (See page IN±27).
BE±336±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)
WhereEverybodyKnowsYourName

OKNG
OKNG
5Check power seat switch.
C
OK
PDisconnect power seat switch connector.
Check continuity of each terminal.
Continuity
Terminal
Switch Position
Side
Neutral
Forward
Back
1342
Replace power seat switch.
6
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 (Passenger's Seat)BE±337
WhereEverybodyKnowsYourName

WIRING DIAGRAM
Buckle Switch Circuit
CIRCUIT DESCRIPTION
Buckle switch signal is sent to ECU when the passenger's seat belt is fastened.
When the signal is input to ECU, ECU prohibits operation of the power wa\
lk±in.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
Check buckle switch.
Check voltage between terminals PBCL
and SGND of ECU connector.
OK
NG
OK
OK NG
NG Proceed to next circuit inspection
shown on matrix chart (See page
BE±319
).
Replace the buckle switch.
Check the harness and connector between
buckle switch and ECU, ECU and battery. Repair or replace harness or
connector.
Check and replace ECU.
BE±338±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)
WhereEverybodyKnowsYourName

NGOK
OKNG
OKNG
INSPECTION PROCEDURE
1Check voltage between terminal PBCL and SGND of ECU connector.
C
OK
PRemote ECU with connectors still connected.
Measure voltage between terminals PBCL and SGND
of ECU connector, when buckle switch is on and off.
With switch ON (Tung plate
is inserted into buckle
switch)With switch OFF (Tung plate is
inserted into buckle switch) Below 1 V
10 ± 14 V
Proceed to next circuit inspection shown on matrix chart
(See page BE±319).
2Check buckle switch.
C
OK
PDisconnect buckle switch connector.
Check continuity between terminal 1 and 2 of buckle
switch connector.
Terminal
Switch
condition
ON
OFF
Continuity
12
Replace buckle switch.
3
Check for open and short in harness and connector between buckle switch and E\
CU, ECU and
battery (See page IN±27).
Repair or replace harness or connector.
Check and replace ECU.
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)BE±339
WhereEverybodyKnowsYourName