seat memory LEXUS SC400 1991 Service Repair Manual

When the negative (±) terminal cable is disconnected from
the battery, memory of the clock and audio systems will be
cancelled. So before starting work, make a record of the con-
tents memorized by each memory system. Then when work
is finished, reset the clock and audio systems as before.
When the vehicle has power tilt and power telescopic steer-
ing, power seat, power outside rear view mirror and power
shoulder belt anchorage, which are all equipped with
memory function, it is not possible to make a record of the
memory contents. So when the operation is finished, it will be
necessary to explain this fact to the customer, and ask the
customer to adjust the features and reset the memory.
To avoid erasing the memory of each memory system, never
use a back±up power supply from outside the vehicle.
3. Even in cases of a minor collision where the airbag does not deploy, the front airbag sensors and the steering wheel pad
should be inspected. (See page AB±9)
4. Never use airbag parts from another vehicle. When replacing parts, replace them with new parts.
5. Before repairs, remove the airbag sensors if shocks are likely
to be applied to the sensors during repairs.
6. The center airbag sensor assembly contains mercury. After
performing replacement, do not destroy the old part. When
scrapping the vehicle or replacing the center airbag sensor
assembly itself, remove the center airbag sensor assembly
and dispose of it as toxic waste.
7. Never disassemble and repair the front airbag sensors, center airbag sensor assembly or steering wheel pad in order
to reuse it.
8. If the front airbag sensors, center airbag sensor assembly or steering wheel pad have been dropped, or if there are cracks,
dents or other defects in the case, bracket or connector,
replace them with new ones.
9. Do not expose the front airbag sensors, center airbag sensor assembly or steering wheel pad directly to hot air or flames.
10. U s e a v o l t / o h m m e t e r w i t h h i g h i m pedance (10 kW/V
minimum) for troubleshooting of the electrical circuit.
11. Information labels are attached to the periphery of the airbag components. Follow the notices.
12. After work on the airbag system is completed, perform the
airbag warning light check (See page AB±30).
±
INTRODUCTION Precautions for Vehicles Equipped with SRS AirbagIN±9
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[2] SYMPTOM CONFIRMATION AND DIAGNOSTIC CODE CHECK
The diagnostic system in the LEXUS SC400 fulfills various functions. The fi\
rst function is the Diagnostic Code
Check in which a malfunction in the signal circuits to the ECU is stored\
in code in the ECU memory at the time
of occurrence, to be output by the technician during troubleshooting. Anot\
her function is the Input Signal Check
which checks if the signals from various switches are sent to the ECU correct\
ly.
The air conditioner system has an Actuator Check function whereby the ECU a\
utomatically operates the actua-
tors of the damper and blowermotor, etc. to check the operation. The cruise control system has a Cancel Si\
gnal
Check function which memorizes and displays what sort of signal it was that l\
ast cancelled the cruise control.
By using these check functions, the problem areas can be narrowed down qui\
ckly and troubleshooting can be
performed effectively. Diagnostic functions are incorporated in the following systems in the \
LEXUS SC400.
SystemDiagnostic CodeCheckInput Signal Check(Sensor Check)Other Diagnosis Function
Engine (with Test Mode)
Automatic Transmission (with Test Mode)
Anti±Lock Brake
Traction Control (Option)
SRS Airbag
Power Seat (only vehicles with memory function)
Wireless Door Lock Control
Cruise Control Cancel Signal
Check
Air Conditioner Actuator Check
In diagnostic code check, it is very important to determine whether the pr\
oblem indicated by the diagnostic code
is still occurring or occurred in the past but returned to normal at pre\
sent. In addition, it must be checked in the
problem sym ptom check whether the malfunction indicated by the diagnostic code is d\
irectly related to the prob-
lem symptom or not. For this reason, the diagnostic codes should be chec\
ked before and after the symptom
confirmation to determine the current conditions, as shown in the table below. If this is not done, it may, depend-
ing on the case, result in unnecessary troubleshooting for normally oper\
ating systems, thus making it more diffi-
cult to locate the problem, or in repairs not pertinent to the problem. Ther\
efore, always follow the procedure in
correct order and perform the diagnostic code check.
DIAGNOSTIC CODE CHECK PROCEDURE
IN±18±
INTRODUCTION How to Troubleshoot ECU Controlled Systems
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GENERAL DESCRIPTION
The LEXUS SC400 is equipped with an SRS (Supplemental Restraint System) a\
irbag.
Failure to carry out service operations in the correct sequence could cause the\
airbag system to unex-
pectedly deploy during servicing, possibly leading to a serious accident.
Further, if a mistake is made in servicing the airbag system, it is possible the\
airbag may fail to operate
when required.
Before performing servicing (including removal or installation of parts, insp\
ection or replacement), be
sure to read the following items carefully, then follow the correct procedure described in the repair
manual.
1. Malfunction symptoms of the airbag system are difficult to confirm, so the diagnostic codes become themost important source of information when troubleshooting.
When troubleshooting the airbag system, always inspect the diagnostic co\
des before disconnecting the
battery (See page AB±25).
2. Work must be started after approx. 20 seconds or longer from the time the ig\
nition switch is turned to the LOCK position and the negative (±) terminal cable is disconnec\
ted from the battery. (The
airbag system is equipped with a back±up power source so that if work is sta\
rted within 20 seconds
of disconnecting the negative (±) terminal cable of the battery, the airbag may be deployed.)
When the negative (±) terminal cable is disconnected from the battery, memory of the clock and audio sys-
tems will be cancelled. So before starting work, make a record of the conten\
ts memorized by the audio
memory system. Then when work is finished, reset the audio systems as before a\
nd adjust the clock. When
the vehicle has power tilt and power telescopic steering, power seat, power \
outside rear view mirror and
power shoulder belt anchorage, which are all equipped with memory function, it\
is not possible to make
a record of the memory contents. So when the work is finished, it will be\
necessary to explain this fact to
the customer, and ask the customer to adjust the features and reset the memory. To avoid erasing the
memory of each memory system, never use a back±up power supply from outside\
the vehicle.
3. Even in cases of a minor collision where the airbag does not deploy, the front airbag sensors and
the steering wheel pad should be inspected (See page AB±9).
4. Never use airbag parts from another vehicle. When replacing parts, replace them with new parts.
5. Before repairs, remove the airbag sensors if shocks are likely to be applied to the sensors during repairs.
6. Never disassemble and repair the front airbag sensors, center airbag sensor a\
ssembly or steering
wheel pad in order to reuse it.
7. If the front airbag sensors, center airbag assembly or steering wheel pa\
d have been dropped, or if there are cracks, dents or other defects in the case, bracket or conn\
ector, replace them with new
ones.
8. Do not expose the front airbag sensors, center airbag sensor assembly or\
steering wheel pad directly to hot air or flames.
9. Use a volt/ohmmeter with high impedance (10 kW/V minimum) for troubleshoo\
ting of the electrical circuit.
10. Information labels are attached to the periphery of the airbag components. Follow t\
he instructions
on the notices.
11. After work on the airbag system is completed, perform the airbag warning\
light check (See page AB±30 ).
AB±2
SRS AIRBAG
± General Description
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DESCRIPTION
The Power Seat Control System carries out seat slide, front vertical, rear \
vertical, reclining and lumbar support
position adjustments electrically. Power seat switch and lumbar support switch.
In addition, operation of the memory switch makes it possible to store the positions of the slide, front vertical,
rear vertical and reclining adjustments in memory and return to the posi\
tion.
The component parts of this system and their function are described in t\
he following table.
 Parts Name\
 \
Function
 








Driver's Seat ECU
\
 
\


\


\


\

\

The seat ECU controls power operation, memory operation, and position re\
turn
operation of the power seat. When input is received from the power seat \
switch,
the relay inside the ECU is controlled and the power seat operates. The \
seat
memory and position return are controlled by mutual communication betwee\
n the
electrically operated Tilt and Telescopic ECU and the seat ECU.
 

Power Seat Switch\
 
\

\

Operation of this switch sends slide, front vertical, rear vertical, rec\
lining signals
to ECU.
 




Driving Position
Memory and Return
Switch\
 
\


\

\

Memory and Return Signals are sent to the seat ECU via the Tilt and Telescopic
ECU.
 






Lumbar Support
Switch
\
 
\


\


\

\

This switch is supplied with power from the DOOR fuse. When the switch i\
s
operated, power is supplied to the lumbar support motor controlling the \
direction
in which the motor turns and turning the current ON and OFF. This switch is not
connected to the ECU and the adjustment position cannot be stored in mem\
ory
for return operation.
 

Position Sensor
\
 
\

\
This sensor sends signals on the position of each motor (slide, front v\
ertical, rear
vertical and reclining) to the ECU for use in memory and return.
 

*Motor
\
 
\

\

These motors operate on current from the driver's seat ECU moving the various
parts of the seat directly. Each motor has a built±in circuit breaker.
*: Slide, Front Vertical, Rear Vertical, Lumbar Support and Reclining.
Motors contained in each seat are described in the following table.
 Motor Slide Front
Vertical
 Rear
Vertical
 Reclining Lumbar
Support 

Seat 

Motor 


Vertical
Motor
 


Vertical
Motor
 


g
Motor 


Support
Motor
 Driver's Seat O* O* O* O* O
*: Operated by the memory and return functions. BE±266
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
WhereEverybodyKnowsYourName

CUSTOMER PROBLEM ANALYSIS CHECK SHEET
POWER SEAT Check Sheet
Inspector 's
Name :
 


 


 

Registration No.
 


 

Customer 's Name
 


 

Registration Year
 

//
 


 


 

Frame No.
 


 

Date Vehicle
Brought In 

//
 

Odometer Reading
 

Km
Miles
 

Condition of
Problem
 

Date Problem
Occurrence\
 

\
//
 



Problem
Occurrence 



How Often does
Problem Occur?
\
 





Continuous
Intermittent ( times a day)
 




 






Manual Function
does not operate
\
 



\



Slide
Front Vertical

Rear Vertical
Reclining
Lumbar Support
 








Symptoms
 










Return Function
does not operate\
 







\



Slide
Front Vertical

Rear Vertical
Reclining

Does not operate in any conditions

Only with key inserted

Only with key not inserted

Only with memory & return switch 1 or 2
 \
 \

Memory function does not operate. 


\
 
\

\


Position return function does not stop when brake pedal is depressed.
For ªReturn function does not operateº malfunctions, check the ret\
urn operation of the items below.
 


Ch k It
 

Tilt & Telescopic
\
 

\


OK
NG
 


Check Item 

Outer Mirror
\
 

\


OK
NG
BE±270±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
WhereEverybodyKnowsYourName

See page
BE±284
BE±28 6
BE±28 8
MATRIX CHART OF PROBLEM SYMPTOMS
Perform troubleshooting of the circuits for the applicable problem symptom in t\
he order given in the chart below.
Proceed to the page located for each circuit.
The Driver's Seat ECU communicates with the tilt & telescopic ECU about memory and \
return, so there are occa-
sions when a power seat problem symptom is caused by trouble in the tilt and telescopic circuit.\
When the
instruction ºSee tilt and telescopic sectionº appears in the matrix chart, pr\
oceed to the matrix chart (see page
SR±28 ) in the tilt and telescopic section and inspect the circuits as direct\
ed by the matrix chart.
BE±276
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
WhereEverybodyKnowsYourName

WIRING DIAGRAM
Position sensor check.OK
Proceed to next circuit inspection
shown on matrix chart (See page
BE±276).
NG
Check position sensor. NG
OK NG
OK Replace position sensor.
Repair or replace harness or
connector.
Check harness and connectors between
ECU and position sensors. (See page
IN±27).
Check and replace ECU.
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.
The ECU uses the number of pulses to constantly calculate
the position relative to the memory position and returns the
seat to the memorized position.
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
BE±294±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
WhereEverybodyKnowsYourName

WIRING DIAGRAM
Check harness and connector between
ECU and tilt & telescopic ECU (See page
IN±27). NG
NG
OK
OK
Check return operation of tilt and
telescopic ECU, and mirror ECU. Repair or replace harness or
connector.
Check and replace tilt &
telescopic ECU.
Proceed to next circuit inspection shown on
matrix chart (See page BE±276).
Serial Communication Circuit
CIRCUIT DESCRIPTION
Memory and return command signals and mutual commu-
nication during return operation pass between the ECU and
the tilt & telescopic ECU in the from of serial data communica-
tion. Signals activating memory and return operation are sent
from the tilt & telescopic ECU to the ECU and mirror ECU.
When the ECU receives a memory signals, its position is
memorized, and when a return signal is received, the position
is returned to the memorized position.
During return operation, tilt & telescopic ECU and ECU continue mutual communi\
cation constantly, and if a mal-
function should occur in the communication wire, the tilt & telescopic ECU stops signal output to the ECU and
stops return operation. However, the tilt & telescopic ECU continues return operation. Even with power \
return
stopped, manual switch operation of the power seat is possible. The mirror ECU receives activation signals only
and is not involved in reciprocal communication during return operation, so\
even when a reply signal from the
ECU to the tilt & telescopic ECU is abnormal and the power seat stops retur\
n operation, the mirror ECU contin-
ues return operation.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BE±306±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
WhereEverybodyKnowsYourName

PRECAUTIONS
Take care to observe the following precautions when performing inspection\
s or removal and replacement
of body electrical related parts.
1. SRS AIR±BAG SYSTEM

Work must be started approx. 20 seconds after the ignition is set to the Loc\
k position and the negative
(±) terminal cable is disconnected from the battery. (See page AB±2)

When disconnecting any of the connectors in the SRS AIR±BAG system, be su\
re to Lock the ignition
switch and disconnect the battery negative (±) terminal first. Since the connectors are twin \
lock type
connectors, disconnect the connectors only after releasing the first stage lock.

When connecting SRS AIR±BAG system connectors, be sure to lock them secur\
ely. (If the connectors
are not locked securely, the system may not operate when needed.)

Always store the steering wheel pad with the pad surface facing upward. (Stor\
ing the pad with its
metallic surface up may lead to a serious accident if the air bag inflates for s\
ome reason.)

When installing the spiral cable, be sure the vehicle is in the straight ahe\
ad condition and confirm that
the spiral cable is in the neutral position when it is installed. (See pag\
e BE±40)

INFORMATION LABELS (NOTICE) are attached to the periphery of the air bag componen\
ts. Follow
the NOTICE.
2. MICRO COMPUTER PRESET DRIVING POSITION SYSTEM
Power Seat Control System
Power Mirror Control System
Power Tilt and Telescopic Steering System

If the battery negative (±) terminal is disconnected, the preset driv\
ing positions stored in memory are
erased, so be sure to note the positions and reset them after the battery termi\
nal is reconnected.
3. AUDIO SYSTEM

If the battery negative (±) terminal is disconnected, the preset AM, F\
M 1 and FM 2 stations stored in
memory are erased, so be sure to note the stations and reset them after the battery terminal is
reconnected.

If the battery negative (±) terminal is disconnected, the ºANTI±\
THEFT SYSTEMº will operate when
the terminal is reconnected, but the radio, tape player and CD player will \
not operate. Be sure to input
the correct ID number so that the radio, tape player and CD player can be o\
perated again.
±
BODY ELECTRICAL SYSTEM PrecautionsBE±7
WhereEverybodyKnowsYourName

Steering Wheel Pad (Airbag and Inflator)
Junction Block No. 1 Center Airbag
Front Airbag Sensor
Front Airbag Sensor
Warning Light Spiral Cable (in Combination Switch)
HANDLING PRECAUTIONS ON RELATED COMPONENTS
1. SRS AIRBAG
Locations of Airbag Components
This vehicle has an SRS AIRBAG (referred to as the airbag in the remain\
der of this manual).
When handling airbag components (removal, installation or inspection, e\
tc.), always follow the directions
given in the repair manual for the relevant model year to prevent the oc\
currence of accidents and airbag
malfunction.
Also take the following precautions when repairing the body:

Work must be started after 20 seconds or longer from the time the ignitio\
n switch is set to the LOCK
position and the negative (-) terminal cable is disconnected from the \
battery.
(The airbag system is equipped with a back-up power source so that if w\
ork is started within 20 seconds
of disconnecting the negative (-) terminal cable of the battery, the airbag may be deployed.)
When the negative (-) terminal cable is disconnected from the battery, memory of the clock and audio
systems will be cancelled. So before starting work, make a record of the\
contents memorized by each
memory system. Then when work is finished, reset the clock and audio sys\
tems as before.
When the vehicle has tilt and telescopic steering, power seat, and outsi\
de rear view mirror, which are all
equipped with memory function, it is not possible to make a record of th\
e memory contents.
So when the operation is finished, it will be necessary to explain this \
fact to the customer, and request
the customer to adjust the features and reset the memory.
To avoid erasing the memory of each memory system, never use back-up powe\
r supply from outside
the vehicle.

When using electric welding, first disconnect the airbag connector (yel\
low color and 2 pins) under the
steering column near the combination switch connector before starting wo\
rk.
Sensor Assembly
INTRODUCTIONIN-6
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