1991 LEXUS SC400 Service Repair Manual

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Page 649 of 4087

LEXUS SC400 1991 Service Repair Manual
Parts Inspection
(Horn Switch)
INSPECTION OF HORN SWITCH
INSPECT HORN SWITCH
(a) Disconnect the negative (±) terminal from the battery.
(b) Remove the left and right covers from the steering wheel

Page 650 of 4087

LEXUS SC400 1991 Service Repair Manual
HORN RELAY
HORN RELAY INSPECTION
INSPECT RELAY CONTINUITY AND OPERATION
If operation is not as specified, replace the relay.
Troubleshooting
You will find the cause of trouble more easily by properly

Page 651 of 4087

LEXUS SC400 1991 Service Repair Manual
POWER SEAT CONTROL SYSTEM
(Drivers seat)
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Drivers Seat)BE±265
WhereEverybodyKnowsYourName

Page 652 of 4087

$LEXUS SC400 1991 Service Repair Manual DESCRIPTION The Power Seat Control System carries out seat slide, front vertical, rear \ vertical, reclining and lumbar support position adjustments electrically. Power seat switch and lumbar support$

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

Page 653 of 4087

LEXUS SC400 1991 Service Repair Manual
PARTS LOCATION
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Drivers Seat)BE±267
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Page 654 of 4087

$LEXUS SC400 1991 Service Repair Manual HOW TO PROCEED WITH TROUBLESHOOTING Perform troubleshooting in accordance with the procedure on the following page.\ CUSTOMER PROBLEM ANALYSIS Using the customer problem analysis check sheet for$

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.
When checking the problem symptoms, pay attention to the following points to\
accurately define the symp-
toms and the extent of the problem:
For ºNot Functioningº problems:
(1) Is the problem only in one part (e.g. ºreclining onlyº), or ever\
ything?
(2) Is the problem only for manual operation, only for position return opera\
tion, or for both manual and position return operation?
(3) Is tilt, telescopic and outer mirror operation normal?
(4) Does the problem occur with the ignition key inserted, or not inserted?
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 each position sensor is correctly input into\
the ECU when the
manual switch is turned ON. The instructions for this diagnosis are included in\
the flow chart for the position
sensor 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 that tilt, telescopic and outer mirror
operation is normal.
BE±268
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
WhereEverybodyKnowsYourName

Page 655 of 4087

LEXUS SC400 1991 Service Repair Manual
BE±270IN±20
BE±276
BE±284 BE±306
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Drivers Seat)BE±269
WhereEverybodyKnowsYourName

Page 656 of 4087

LEXUS SC400 1991 Service Repair Manual
CUSTOMER PROBLEM ANALYSIS CHECK SHEET
POWER SEAT Check Sheet
Inspector s
Name :

Registration No.

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

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