1991 LEXUS SC400 wiring

WIRING DIAGRAM
Terminal of ECU
No.SymbolTerminal NameNo.SymbolTerminal Name
P12±1SYSBPower SourceP12±10PFSWReclining Front Limit Switch
2SLSWSlide Limit Switch11SSRSSlide Sensor
3PVCCPosition Sensor Power Source12PBCLPassenger's Buckle Switch
4DOUT±±13RRSWReclining Rear Limit Switch
5SLDRSlide Switch (Back)14CHKCheck
6SLDFSlide Switch (Forward)15SGNDSensor Ground
7SLD+Slide Motor (Forward)16GNDGround
8+BPower Source17SLD±Slide Motor (Back)
9PRDCTension Reducer18
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)BE±317
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STANDARD VALUE OF ECU TERMINAL
 

Terminals 

Symbols 


Wiring
Color 

Condition 

Standard Value
 P12±1
eP12±16 SYS eBGND Re W±B Always 10 ~ 14 V
 

P12±2
e
 

SLSW
e
 

V±W
e
 


Slide neutral limit switch OFF
(Passenger's seat is slided at most back position, when
power seat operation) 

10 ~ 14 V
 




P12 2
e
Body Ground 




SLSW
e
Body Ground 




VW
e
Body Ground 




Slide neutral limit switch ON
(Passenger's seat is slided 120 mm or more from most
back position, when power seat operation) 




Below 1 V
P12±3
eP12±15PVCC eSGNDVe BRAlways (When power seat operation)10 ~ 14 V P12±4 DOUT ' ' ' 
P12 eP12 16
 
SLDR eGND
 
LR eWB
 Slide switch is pushed back 10 ~ 14 V P12 eP12±16 SLDR eGND L±R eW±B Others Below 1 V
 
P12 6 eP12 16
 
SLDF eGND
 
LY eWB
 Slide switch is pushed forward 10 ~ 14 V
 P12±6 eP12±16 SLDF eGND L±Y eW±B Others Below 1 V
 P12 7 eP12 16 SLD+ eGND Le WB Slide switch is pushed forward 10 V ~ 14 V
 P12±7 eP12±16 SLD+ eGND Le W±B Others Below 1 V
P12±8 eP12±16+B eGNDL±W eW±BAlways10 ~ 14 V 

P12±9
e
 

PRDC
e
 

B
e
 

Passenger's buckle switch ON and ignition switch ON
(Tung plate is inserted into buckle switch) 

Below 1 V
 


P12 9
e
Body Ground 


PRDC
e
Body Ground 


B
e
Body Ground 


Passenger's buckle switch OFF and Ignition switch ON
(Tung plate is not inserted into buckle switch) 

10 ~ 14 V
 

P12±10
e
 

RFSW
e
 

Y
e
 


Reclining front limit switch OFF (Passenger's seat
back is moved backward, when power seat operation) 

10 ~ 14 V
 
P12 10
e
Body Ground 
RFSWe
Body Ground 
Ye
Body Ground Reclining front limit switch ON (Passenger's seat
back is moved forward, when power seat operation) Below 1 V
 

P12±11
eP12±15
 

SSRS
eSGND
 

LG
eBR
 


When passenger's seat is sliding back and forth,
when power seat operation 

0
e 12 V
 

P12±12
e
 

PBCL
e
 

B±Y
e
 


Passenger's buckle switch OFF (Tung plate is not
inserted into buckle switch, when power seat operation) 

10 ~ 14 V
 
P12 12
e
Body Ground 
PBCLe
Body Ground 
BYe
Body Ground Passenger's buckle switch ON (Tung plate is inserted
into buckle switch, when power seat operation) Below 1 V
 


P12 13
eP12 16
 


PRSW
eGND
 


LG R
eWB
 

Reclining rear limit switch OFF (Passenger's seat
back is moved backward, when power seat operation) 

10 ~ 14 V
 


P12±13
eP12±16 


PRSW
eGND 


LG±R
eW±B 


Reclining rear limit switch ON (Passenger's seat
back is moved forward, when power seat operation) 

Below 1 V
 P12±14 CHK ' ' '
P12±15
eSGNDeBReAlways1
or less Body Ground Body Ground Body Ground Always 1
or less
 P12±16 e GNDe W±Be 
Always
 
1
or less Body Ground Body Ground Body Ground Always 1
or less
 
P12 17 eP12 16
 
SLD eGND
 
LB eWB
 Slide switch is pushed back 10 ~ 14 V
 P12±17 eP12±16 SLD± eGND L±B eW±B Others Below 1 V
 P12±18 ' ' ' '
BE±318±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)
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WIRING DIAGRAM
CIRCUIT INSPECTION
ECU Power Source Circuit
CIRCUIT DESCRIPTION
This circuit provides power for ECU operation and is also the power source f\
or the slide position sensor.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
Check DOME fuse.NG
OK
NG NG
OK
OK Check for short in all the harness
and components connected to
DOME fuse. (See attached wir-
ing diagram).
Check voltage between terminals SYSB and
GND of ECU connector. Proceed to next circuit inspection
shown on matrix chart.
(See page
BE±319).
Check continuity between terminal GND of
ECU connector and body ground. Repair or replace harness or
connector.
Check and repair harness or connector
between ECU and battery.
BE±324±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)
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Check DOOR fuse.NG
OK
NG
OK NGOK Check for short in all the harness
and components connected to
the DOOR fuse (See attached
wiring diagram). *
1
Check voltage between terminals +B and
GND of ECU connector.
Proceed to next circuit inspection
shown on matrix chart (See page
BE±319
).
Check continuity between terminal GND of
ECU connector and body ground. Repair or replace harness of
connector.
Check and repair harness or connector
between ECU and battery. *
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 fuse may become open, so also in-
spect the actuator. (Slide motor circuit on
page
BE±328 ).
WIRING DIAGRAM
Slide Motor Power Source Circuit
CIRCUIT DESCRIPTION
This is the power source for slide motor.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BE±326±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)
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OKNG
NGOK
OKNG
INSPECTION PROCEDURE
1Check DOOR fuse.
Check for short in all the harness components con-
nected to the DOOR fuse and repair them (See attached
wiring diagram). *1
2Check voltage between terminals +B and GND of ECU connector.
C
OK
PRemove passenger's seat ECU with connectors still
connected.
Measure voltage between terminals +B and GND of
ECU connector.
Voltage: 10 ± 14 V
Proceed to next circuit inspection shown on matrix chart
(See page BE±319).
3Check continuity between terminal GND of ECU connector and body ground.
C
OK
Measure resistance between terminal GND of ECU and
body ground.
Resistance: 1
or less
Repair or replace harness or connector.
Check and repair harness or connector between
ECU and battery.
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)BE±327
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WIRING DIAGRAM
Slide Motor Circuit
CIRCUIT DESCRIPTION
The passenger's seat ECU control the slide motor.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
Check slide motor.NG
NG
OK
OK Replace motor.
Repair or replace harness or
connector.
Check harness and connector between
ECU and motor (See page
IN±27).
Proceed to next circuit inspection shown
on matrix chart (See page BE±319).
BE±328±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)
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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)
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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