1991 LEXUS SC300 code 32

PRECAUTIONS FOR VEHICLES
EQUIPPED WITH SRS AIRBAG
The LEXUS SC400 is equipped with an SRS (Supplemental Re-
straint System) airbag.
Failure to carry out service operations in the correct sequence
could cause the airbag system to unexpectedly deploy during serv-
icing, possibly leading to a serious accident.
Further, if a mistake is made in servicing the airbag system, it is pos-
sible the airbag may fail to operate when required.
Before performing servicing (including removal or installation of
parts, inspection or replacement), be sure to read the following
items carefully, then follow the correct procedure described in this
manual.
Locations of Airbag Components
1. Malfunction symptoms of the airbag system are difficult to confirm,
so the diagnostic codes become the most important source of
information when troubleshooting.
When troubleshooting the airbag system, always inspect the diag-
nostic codes before disconnecting the battery. (See page
AB±25)
2. Work must be started after approx. 20 seconds or longer from the time the ignition switch is turned 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 work is started within 20 seconds of disconnecting
the negative (±) terminal cable of the battery, the airbag may be
deployed.)
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INTRODUCTION Precautions for Vehicles Equipped with SRS Airbag
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FRONT AIRBAG SENSOR
1. Never reuse the front airbag sensors involved in a collisionwhen the airbag has deployed. (Replace both the left and
right airbag sensors.)
2. Install the front airbag sensor with the arrow on the sensor facing toward the front of the vehicle.
3. The front airbag sensor set bolts have been anti±rust treated. When the sensor is removed, always replace the set bolts
with new ones.
4. The front airbag sensor is equipped with an electrical connection check mechanism. Be sure to lock this
mechanism securely when connecting the connector. If the
connector is not securely locked, a malfunction code will be
detected by the diagnosis system (See page AB±10).
SPIRAL CABLE (IN COMBINATION
SWITCH)
The steering wheel must be fitted correctly to the steering column
with the spiral cable at the neutral position; otherwise cable dis-
connection and other troubles may result. Refer to page AB±15
of this manual concerning correct steering wheel installation.
STEERING WHEEL PAD (WITH AIRBAG)
1. When removing the steering wheel pad or handling a new steering wheel pad, it should be placed with the pad top
surface facing up.
In this case, the twin±lock type connector lock lever should
be in the locked state and care should be taken to place it so
the connector will not be damaged. And do not store a steer-
ing wheel pad on top of another one. (Storing the pad with its
metallic surface up may lead to a serious accident if the air-
bag inflates for some reason.)
2. Never measure the resistance of the airbag squib. (This
may cause the airbag to deploy, which is very
dangerous.)
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INTRODUCTION Precautions for Vehicles Equipped with SRS Airbag
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HOW TO PROCEED WITH TROUBLESHOOTING
Carry out troubleshooting in accordance with the procedure on the follow\
ing page. Here, only the basic proce-
dure is shown. Details are provided in each section, showing the most effective methods for each circuit. Confirm
the troubleshooting procedures first for the relevant circuit before beginn\
ing troubleshooting of that circuit.


Ask the customer about the conditions and the
environment when the problem occurred.
\b 
Confirm the symptoms and the problem
conditions, and check the diagnostic codes.
(When the problem symptoms do not appear
during confirmation, use the symptom simu-
lation method described later on.)
  
Check the result obtained in Step \b, then
confirm the inspection procedure for the sys-
tem or the part which should be checked us-
ing the diagnostic code chart or the matrix
chart of problem symptoms.

Check and repair the affected system or part
in accordance with the instructions in Step .

After completing repairs, confirm that the
problem has been eliminated.
(If the problem is not reproduced, perform the
confirmation test under the same conditions
and in the same environment as when it oc-
curred for the first time.)
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INTRODUCTION How to Troubleshoot ECU Controlled Systems
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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
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INTRODUCTION How to Troubleshoot ECU Controlled Systems
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Taking into account the above points, a flow chart showing how to proceed with\
troubleshooting using the diag-
nostic code check is shown below. This flow chart shows how to utilize the diagnostic code check effectively,
then by carefully checking the results, indicates how to proceed either to d\
iagnostic code troubleshooting or to
troubleshooting of problem symptoms.
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[4] DIAGNOSTIC CODE CHART
The inspection procedure is shown in the table below. This table permits efficient and accurate troubleshooting
using the trouble codes displayed in the diagnostic code check. Proceed with \
troubleshooting in accordance
with the inspection procedure given in the diagnostic chart corresponding to the trouble codes displayed. The
engine diagnostic code chart is shown below as an example.
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INTRODUCTION How to Troubleshoot ECU Controlled Systems
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[5] MATRIX CHART OF PROBLEM SYMPTOMS
The suspect circuits or parts for each problem symptom are shown in the tab\
le below. Use this table to trouble-
shoot the problem when a ºNormalº code is displayed in the diagnostic code check but\
the problem is still occur-
ring. Numbers in the table indicate the inspection order in which the circuit\
s or parts should be checked.
HINT: When the problem is not detected by the diagnostic system even though t\
he problem symptom is present,
it is considered that the problem is occurring outside the detection ran\
ge of the diagnostic system, or that the
problem is occurring in a system other than the diagnostic system.
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HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION
PROCEDURE
1. For troubleshooting, diagnostic code charts or problem symptom charts are p\
rovided for each circuit withdetailed inspection procedures on the following pages.
2. When all the component parts, wire harnesses and connectors of each circuit \
except the ECU are found to be normal in troubleshooting, then it is determined that the problem \
is in the ECU.
Accordingly, if diagnosis is performed without the problem symptoms occurring, the \
instruction will be to
check and replace the ECU, even if the problem is not in the ECU. So, al\
ways confirm that the problem
symptoms are occurring, or proceed with inspection while using the sympt\
om simulation method.
3. The instructions ºCheck wire harness and connectorº and ºCheck and\
replace ECUº which appear in the inspection procedure, are common and applicable to all diagnostic codes.\
Follow the procedure outlined
below whenever these instructions appear.
Check Wire Harness and Connector
The problem in the wire harness or connector is an open circuit or a short \
circuit.
OPEN CIRCUIT:
This could be due to a disconnected wire harness, faulty contact in the conn\
ector, a connector terminal pulled
out, etc.
HINT:
1. It is rarely the case that a wire is broken in the middle of it. Most cases occur at the connector. Inparticular, carefully check the connectors of sensors and actuators.
2. Faulty contact could be due to rusting of the connector terminals, to foreign materials entering terminals or a drop in the contact pressure between the male and female terminals of th\
e connector.
Simply disconnecting and reconnecting the connectors once changes the conditio\
n of the
connection and may result in a return to normal operation.
Therefore, in troubleshooting, if no abnormality is found in the wire harness and \
connector check, but the prob-
lem disappears after the check, then the cause is considered to be in th\
e wire harness or connectors.
SHORT CIRCUIT:
This could be due to a short circuit between the wire harness and the body ground or t\
o a short inside the switch,
etc.
HINT:
w When there is a short between the wire harness and body ground, check thorou\
ghly whether the wire
harness is caught in the body or is clamped properly.
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INTRODUCTION How to Troubleshoot ECU Controlled SystemsIN±27
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