ECU LEXUS SC400 1991 Service Repair Manual

 
Parts Name\
 \
Function
 


Passenger's Seat
ECU\
 
\

\

The passenger seat ECU controls the distance the seat slides when the po\
wer seat switch is
operated and also controls the power slide distance during return operat\
ion.
 

Power Seat Switch\
 
\

\

When the power seat switch is operated, a seat slide signal is sent to t\
he ECU. The reclining
slide of the switch is linked directly to the motor operation.
 

Slide Position Sensor\
 
\

\

The slide position sensor detects the slide distance during walk±in o\
peration and
inputs the information to the ECU.
 


Slide Neutral Limit
Switch\
 
\

\

This switch detects the neutral position of the seat slide and input the\
information to the ECU.
 


Reclining Front Limit
Switch\
 
\

\

This switch detects when the seatback is inclined fully forward and info\
rms the
ECU.
 


Reclining Rear Limit
Switch\
 
\

\

This switch detects when the seatback is pulled back and informs the ECU\
.
 Motor\
 \
There are two motors, one each for seat sliding and for reclining.
 


Tension Reducer and
Buckle Switch\
 
\

\

This switch inputs a signal to the ECU to inform it whether the tongue o\
f the
passenger's seat belt is inserted in the buckle.
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)BE±311
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HOW TO PROCEED WITH TROUBLESHOOTING
Perform troubleshooting in accordance with the procedure on the following page.\

CUSTOMER PROBLEM ANALYSIS
Using the customer problem analysis check sheet for reference, ask the c\
ustomer in as much detail as
possible about the problem.
\b PROBLEM SYMPTOM CONFIRMATION,  SYMPTOM SIMULATION.
Confirm the problem symptoms. If the problem does not reappear, be sure to simulate the problem using
the ºProblem Simulation Methodsº.
 MATRIX CHART OF PROBLEM SYMPTOMS
Confirm the order of inspection on the matrix chart for the particular problem symptom involved. For ºNot
Functioningº problems, pay attention to the points in \b to find out the specifics of the problem, then choose
the most appropriate problem symptom from among those listed on the matr\
ix chart, and proceed with trou-
bleshooting accordingly.
 CIRCUIT INSPECTION
Proceed with diagnosis of each circuit in accordance with the inspection order \
confirmed in . Determine
whether the cause of the problem is in the sensor, actuators, wire harness and connectors, or the ECU.
 POSITION SENSOR CHECK
This function checks that the signal from position sensor is correctly input\
into the ECU. The instructions
for this diagnosis are included in the flow chart for the position senso\
r circuit.
 REPAIR
After the cause of the problem is located, perform repairs by following the i\
nspection and replacement pro-
cedures is this manual.
 CONFIRMATION TEST
After completing repairs, confirm that the problem is eliminated and pow\
er walk±in operation is normal.
BE±314
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)
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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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OKNG
NGOK
OKNG
INSPECTION PROCEDURE
1Check DOME fuse.
Check for short in all the harness and components con-
nected to DOME fuse and repair them (See attached wir-
ing diagram).
2Check voltage between terminals SYSB and GND of ECU connector.
C
OK
PRemove ECU with connectors still connected.
Measure voltage between terminals SYSB 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 con-
nector 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±325
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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)
WhereEverybodyKnowsYourName

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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OKNG
OKNG
INSPECTION PROCEDURE
1Check Slide Motor.
C
OK
P(1) Remove Seat
(2) Disconnect slide motor connector.
Check seat movement when battery voltage is applied
to slide motor.
Connect positive
(negative  ) terminal to terminal 1
of slide motor connector and negative  (positive
)
terminal to terminal 2.
Terminal
Movement
Forward
Back
12
Replace motor.
2Check for open and short in harness and connector between ECU and motor (See\
page IN±27).
Repair or replace harness or connector.
Proceed to next circuit inspection shown on ma-
trix chart (See page BE±319).
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)BE±329
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