1991 LEXUS SC400 sensor

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
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BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)BE±317
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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)
WhereEverybodyKnowsYourName

WIRING DIAGRAM
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.
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
Inspect the circuit which is malfunctioning.
Position sensor check.OK
NG
OK
OK NG
NG Proceed to next circuit inspection
shown on matrix chart (See page
BE±319
)
Replace position sensor.
Check position sensor.
Check harness and connectors between
ECU and position sensor (See page IN±27). Repair or replace harness or
connector.
Check and replace ECU.
BE±330±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)
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INSPECTION PROCEDURE
1Position Sensor Check.
C
Hint
P(1) Remove the passenger's seat.
(2) Remove the bolts for seat rail and lift the seat cush-ion up a little.
Notice: If the seat cushion is lifted too 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.
Position sensor check
(1) Connect terminal CHK of the ECU to body ground to put the ECU into check mode.
(2) Measure voltage between terminal DOUT of ECU and body ground.
Use an analog type meter.
(3) Check that the ªreadyº code is output as shown in the illustration.
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)BE±331
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NGOK
1Position sensor check (Cont'd).
OK
Hint
(4) Operate the power seat manual switch and checkthe change in the voltage when the seat is moving.
(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 headrest reaches the highest or lowest
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
NG
OK Code
NG Code
Proceed to next circuit inspection shown on the matrix
chart (See page BE±318).
Go to step [2].
BE±332±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger'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 the 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 differ-
ent position each time.)
half of battery
voltage
Replace position sensor.
3
Check for open and short in harness and connectors between ECU and posit\
ion sensor (See
page IN±27 ).
Repair or replace harness or connectors.
Check and replace ECU.
±
BODY ELECTRICAL SYSTEM Power Seat Control System (Passenger's Seat)BE±333
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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.
 PROBLEM SYMPTOM CONFIRMATION,  SYMPTOM SIMULATION
Confirm the problem symptoms. If the problem does not reappear, be sure to simulate the problem using
ºProblem Simulation Methodº.
For example, if the malfunction involves failure of the lock or unlock duri\
ng operation of the Door Lock Con-
trol Switch, check if lock and unlock operation of the door using the key is\
normal or abnormal, and also
check if key confinement prevention function and luggage compartment door ope\
ner function are normal
or not. And having fully checked the extent of the malfunction.
 MATRIX CHART OF PROBLEM SYMPTOMS
Confirm the order of inspection for each applicable problem symptom on t\
he matrix chart.
 CIRCUIT INSPECTION
Proceed with diagnosis of each circuit in accordance with the inspection order \
confirmed in . Judge
whether the cause of the problem is in the sensor, wire harness and connectors, or the ECU.
 REPAIR
When the cause of the problem is found in , perform repairs.
 CONFIRMATION TEST
After completing repairs, confirm that the problem is eliminated and that all functions of the door lock control
system are normal.
BE±364
±
BODY ELECTRICAL SYSTEM Door Lock Control System
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