LEXUS SC400 1991 Service Repair Manual

Check stop light operation.NG
OK OK
NG Check stop light circuit
(See page
BE±64).
Proceed to next circuit inspection
shown on matrix chart
(See page
BE±276).
Check voltage between terminals STOP
of ECU connector and body ground.
Check and repair harness and connec-
tor between ECU and stop light switch.
WIRING DIAGRAM
Stop Light Circuit
CIRCUIT DESCRIPTION
The stop light switch sends a brake ON of Off signal to the ECU. When the ECU receives a brake ON signal
it prohibits return of the seat.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BE±298±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
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OKNG
NGOK
INSPECTION PROCEDURE
1Check stop light operation.
Check that the stop light comes on when the brake pedal is depressed, and turn\
s off when the pedal
is released.C
Check stop light circuit. (See page BE±64).
2Check voltage between terminal STOP of ECU connector and body ground.
C
OK
Hint
PRemove ECU with connectors still connected.
Measure voltage between terminal STOP of ECU and
body gr ound when the brake pedal is depressed and re-
leased.
Brake pedal Voltage
Depressed 10 ± 14 V Released Below 1 V
Proceed to next circuit inspection shown on matrix chart
(See page BE±276).
Check and repair harness and connector between
ECU and stop light switch.
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)BE±299
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WIRING DIAGRAM
Check shift position indicator. NGOK
OK
NG Check shift position indicator
circuit (See page BE± 141).
Check voltage between terminal P of ECU
connector and body ground. Proceed to next circuit inspection
shown on matrix chart (See page
BE±276
).
Check and repair harness and connector
between ECU and connector.
Neutral Start Switch Circuit
CIRCUIT DESCRIPTION
The neutral start switch detects when the shift position is in P range and \
sends a signal to the ECU.
When the return switch is turned ON with the IG SW ON and the shift in P\
range, the ECU performs
return operation.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BE±300±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
WhereEverybodyKnowsYourName

OKNG
NGOK
INSPECTION PROCEDURE
1Check the shift position indicator.
Check that P lights up on the shift indicator when P range is shifted in\
to, and that P is OFF when
shiftin
g into another range.
C
Check shift position indicator circuit (See page BE±141).
2Check voltage between terminal P of ECU connector and body ground.
C
OK
PRemove ECU with connectors still connected.
(1) Turn ignition switch ON.
(2) Measure voltage between terminal P of ECU con-nector and body ground when the shift lever is posi-
tioned to the following ranges.
Shift range
P
1
0
Other than PVoltage
10 ± 14 V
Below 1 V
Proceed to next circuit inspection shown on matrix chart
(See page BE±276).
Check and repair harness and connector between
ECU and connector.
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)BE±301
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WIRING DIAGRAM
Ignition Switch Circuit
CIRCUIT DESCRIPTION
This circuit sends an ignition switch ON or OFF signal to the ECU.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
Check ECU±IG fuse.NG
Check for short in all the harness
and components connected to
ECU±IG fuse.
Check voltage between terminal IG of
ECU connector and body ground. OK
OK
NG Proceed to next circuit inspection
shown on matrix chart
(See page
BE±276).
Check and repair harness or connector
between ECU and battery (See page IN±27).
BE±302±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
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OKNG
NGOK
INSPECTION PROCEDURE
1Check ECU ± IG fuse.
Check for short in all the harness and components con-
nected to ECU±IG fuse.
2Check voltage between terminal IF of ECU connector and body ground.
C
PRemove ECU with connectors still connected.
Measure voltage between terminal IG of ECU connector
and body ground when ignition switch is on and off.
Ignition switch Voltage
ON
OFF 10 ± 14 V
Below 1 V
Proceed to next circuit inspection shown on matrix chart
(See page BE±276).
Check and repair harness or connector between
ECU and battery (See page IN±27).
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)BE±303
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WIRING DIAGRAM
Check voltage between each termi-
nal and a SGND of ECU connector.OK
NG NG
NG
OK
OK
Check power seat switch.
Replace power seat switch.Proceed to next circuit inspection
shown on matrix chart (See page
BE±276).
Check harness and connectors between
ECU and power seat switch (See page
IN±27).Repair or replace harness
or connector.
Check and replace ECU.
Power Seat Switch Circuit
CIRCUIT DESCRIPTION
When the power seat switch is operated, a signal is sent from the power seat\
switch to the ECU and the ECU
sends a signal to the motor to make it operate (except for the lumbar s\
upport).
Even if a malfunction should occur with the position sensor and return opera\
tion is prohibited, manual operation
will occur as normal.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BE±304±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)
WhereEverybodyKnowsYourName

NGOK
OKNG
OKNG
INSPECTION PROCEDURE
1Check voltage between each terminal and SGND ECU connector.
C
OK
PRemove ECU with connectors still connected.
Measure voltage between each terminal of the manual
switch and SGND of ECU connector.
At each terminalWith SW ON Below 1 V
With SW OFF 10 ± 14 V
Proceed to next circuit inspection shown on matrix chart
(See page BE±276).
2Check power seat switch.
C
PDisconnect power seat switch connector.
Check continuity of each terminal.
Replace power seat switch.
3
Check for open and short in harness and connectors between ECU and power seat\
switch (See
page IN±27 ).
Repair or replace harness or connector.
Check and replace ECU.
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)BE±305
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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)
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OKNG
OKNG
INSPECTION PROCEDURE
1Check for open and short in harness and connector between ECU and tilt & telescopi\
c ECU (See
page IN±27 ).
HintDepending on the differences that exist for return opera-
tion or non±return operation of each system, the prob-
lems is the harness and connector shown in the table
below may be considered.
Trouble areaTilt &
TelescopicMirrorSeat
Open
Short
Open
Open or Short
Repair or replace harness or connector.
2Check return operation by tilt & telescopic ECU, and mirror ECU.
Check that return operation is normal for tilt, telescopic and mirror fu\
nctions.C
Check and replace tilt & Telescopic ECU.
Proceed to next circuit inspection shown on
matrix chart (See page BE±276).
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Driver's Seat)BE±307
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