LEXUS SC400 1991 Service Repair Manual

OKNG
NGOK
OKNG
INSPECTION PROCEDURE
1Check DOME fuse.
Check for short in all the harness and components con-
nected to the DOME fuse (See attached wiring diagram).
2Check voltage between terminals SYSB and SGND of ECU connector.
C
OK
PRemove ECU with connectors still connected.
Measure voltage between terminals SYSB and SGND
of ECU connector.
Voltage: 10 ± 14 V
Proceed to next circuit inspection shown on matrix chart
(See page BE±276).
3Check continuity between terminal SGND of ECU connector and body ground.\
C
OK
Measure resistance between terminal SGND of ECU
connector and body ground.
Resistance: 1
or less.
Repair or replace harness or connector.
Check and repair harness or connector between
ECU and battery.
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BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)BE±287
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WIRING DIAGRAM
Motor Circuit
CIRCUIT DESCRIPTION
The driver's seat ECU controls the 4 motors for slide, front vertical, rear vertica\
l and reclining.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
Inspect the circuit of the motor which is malfunctioning.
Check motor.NG Replace motor.
OK
Check harness and connector between
ECU and motor (See page IN±27). NG
OK Repair or replace harness or
connector.
Proceed to next circuit inspection shown
on matrix chart (See page BE±276).
BE±288
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BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
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INSPECTION PROCEDURE
1Check Motor
Slide
Front vertical
Rear vertical
OK
P
OK
OK
C
(1) Remove seat.
(2) Disconnect each motor connector.
Check seat movement when battery voltage is applied
to each motor.
Slide
Front vertical
Rear vertical
Terminal
Terminal
Terminal
Movement
Movement
Movement
Cushion rises
Forward
Back
Cushion lowers
Cushion rises
Cushion lowers
12
2
2
1
1
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BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)BE±289
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OKNG
OKNG
RecliningOKReclining
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
matrix chart (See page BE±276).
BE±290±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
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WIRING DIAGRAM
Position Sensor Power Source Circuit
CIRCUIT DESCRIPTION
This circuit provides power to the slide, front vertical, rear vertical and \
reclining sensors.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
Check voltage between terminals PVCC
of ECU connector and body ground.OK
Proceed to next circuit inspection
shown on matrix chart (See page
BE±276
).
NG
NG
OK
Check harness and connector connected to
terminal PVCC of ECU (See page IN±27).Repair or replace harness or
connector.
Check and replace ECU.
BE±292
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BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
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NGOK
OKNG
INSPECTION PROCEDURE
1 Check voltage between terminal PVCC of ECU connector and body ground.
C
OK
PRemove ECU with connectors still connected.
While operating the manual switch and moving the seat,
check voltage between terminal PVCC of ECU connec-
tor and body ground.
Voltage: 7 ± 9 V
Proceed to next circuit inspection shown on matrix chart
(See page BE±276).
2
Check for open and short in harness and connector connected to terminal PVCC \
of ECU (See
page IN±27 ).
Check for open or short in the har-
nesses or connectors for the position
sensor power source circuit outlined
in the diagram with a thick line ( ').
Repair or replace harness or connector.
Check and replace ECU.
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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
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BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
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INSPECTION PROCEDURE
1Position sensor check
C
P(1) Remove the driver's seat.
(2) Remove the bolts for the front vertical adjuster andlift the seat cushion up a little.
Notice: If the seat cushion is lifted to 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.
(1) Connect terminal CHK of the ECU to body ground to put the ECU into check mode.
(2) Measure the voltage between terminal SO of ECU and body ground.
HINT: Use an analog type meter.
(3) Check that the ªreadyº code is output as shown in the illustration.
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1Position sensor check (Cont'd)
OK Code
NG Code
OK
Hint
Hint
(4) Operate the power seat switch and check thechange in the voltage when the seat is moving.
The lumbar support does not have a position sensor, so
the sensor check cannot be done.
(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 slide position reaches the most forward
or back 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 Code
NG Code
OK
NG
BE±296±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
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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 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 different
position each time
.)
half of battery
voltage
Replace position sensor.
3
Check for open and short in harness and connectors between ECU and position s\
ensors (See
page IN±27 ).
Repair or replace harness or connectors.
Check and replace ECU.
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BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)BE±297
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