1991 LEXUS SC400 Section 27

HOW TO USE THIS MANUAL
INDEX
An INDEX is provided on the first page of each sec-
tion to guide you to the item to be repaired.
To assist you in finding your way through the manual,
the Section Title and major heading are given at the
top of every page.
ALPHABETICAL INDEX
An ALPHABETICAL INDEX is also provided at the
end of this manual so that you can rapidly find the
item and page you are searching for.
GENERAL DESCRIPTION
At the beginning of each section, a General Descrip-
tion (Precautions) is given that pertains to all repair
operations contained in that section.
Read these precautions before starting any
repair task.
REPAIR PROCEDURES
Most repair operations begin with an overview il-
lustration. It identifies the components and shows
how the parts fit together.
Example:
PREPARATION
Preparation lists the SST (Special Service Tools), rec-
ommended tools, equipment, lubricant and SSM
(Special Service Materials) which should be prepared
before beginning the operation and explains the pur-
pose of each one.
TROUBLESHOOTING
TROUBLESHOOTING tables are included for each
system to help you diagnose the problem and find the
cause.
The fundamentals of how to proceed with trouble±
shooting are described on page IN±15. Be sure to
read this before performing troubleshooting.
IN±2
±
INTRODUCTION How To Use This Manual
WhereEverybodyKnowsYourName

The procedures are presented in a step±by±step format:
wThe illustration shows what to do and where to do it.
w The task heading tells what to do.
w The detailed text tells how to perform the task and gives
other information such as specifications and warnings.
Example:
This format provides the experienced technician with a FAST
TRACK to the information needed. The upper case task
heading can be read at a glance when necessary, and the
text below it provides detailed information. Important specifi-
cations and warnings always stand out in bold type.
REFERENCES
References have been kept to a minimum. However, when
they are required you are given the page to refer to.
SPECIFICATIONS
Specifications are presented in bold type throughout the text
where needed. You never have to leave the procedure to look
up your specifications. They are also found at the end of each
section, for quick reference.
CAUTIONS, NOTICES, HINTS:
w CAUTIONS are presented in bold type, and indicate
there is a possibility of injury to you or other people.
w NOTICES are also presented in bold type, and indicate
the possibility of damage to the com ponent being
repaired.
w HINTS are separated from the text but do not appear in
bold. They provide additional information to help you
efficiently perform the repair.
SI UNIT
The UNIT given in this manual are primarily expressed with
the SI UNIT (International System of Unit), and alternately ex-
pressed in the metric system and in the yard/pound system.
Example:
Torque: 30 N Vm (310 kgf Vcm, 22 ft Vlbf)
±
INTRODUCTION How to Use This ManualIN±3
WhereEverybodyKnowsYourName

5. Non±reusable parts(a) Always replace cotter pins, gaskets, O±rings and oilseals etc. with new ones.
(b) Non±reusable parts are indicated in the component
illustrations by the º º symbol.
6. Precoated parts Precoated parts are bolts and nuts, etc. that are coated with
a seal lock adhesive at the factory.
(a) If a precoated part is retightened, loosened or causedto move in any way, it must be recoated with the
specified adhesive.
(b) Recoating of precoated parts
(1) Clean off the old adhesive from the bolt, nut or threads.
(2) Dry with compressed air.
(3) Apply the specified seal lock adhesive to the bolt or nut threads.
(c) P re co a te d pa rts are in d ica te d in th e co m ponent
illustrations by the º
º symbol.
7. When necessary, use a sealer on gaskets to prevent leaks.
8. Carefully observe all specifications for bolt tightening
torques. Always use a torque wrench.
9. Use of special service tools (SST) and special service materials (SSM) may be required, depending on the nature
of the repair. Be sure to use SST and SSM where specified
and follow the proper work procedure. A list of SST and SSM
can be found in the preparation part at the front of each
section in this manual.
10. When replacing fuses, be sure the new fuse has the correct
amperage rating. DO NOT exceed the rating or use one with
a lower rating.
11. Care must be taken when jacking up and supporting the vehicle. Be sure to lift and support the vehicle at the proper
locations (See page IN±33).
(a) If the vehicle is to be jacked up only at the front or rear end, be sure to block the wheels at the opposite end in
order to ensure safety.
(b) After the vehicle is jacked up, be sure to support it on
stands. It is extremely dangerous to do any work on a
vehicle raised on a jack alone, even for a small job that
can be finished quickly.
±
INTRODUCTION General Repair InstructionsIN±5
WhereEverybodyKnowsYourName

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.)
IN±16
±
INTRODUCTION How to Troubleshoot ECU Controlled Systems
WhereEverybodyKnowsYourName

[1] CUSTOMER PROBLEM ANALYSIS
In troubleshooting, the problem symptoms must be confirmed accurately and \
all preconceptions must be
cleared away in order to give an accurate judgment. To ascertain just what the problem symptoms are, it is ex-
tremely important to ask the customer about the problem and the conditions at t\
he time it occurred.
Important Points in the Problem Analysis
The following 5 items are important points in the problem analysis. Past pr\
oblems which are thought to be unre-
lated and the repair history, etc. may also help in some cases, so as much information as possible s\
hould be
gathered and its relationship with the problem symptoms should be correctly asce\
rtained for reference in trou-
bleshooting. A customer problem analysis table is provided in the troubl\
eshooting section for each system for
your use.
Important Points in the Customer Problem Analysis
wWhat Vehicle model, system name
w When Date, time, occurrence frequency
w Where Road conditions
w Under what conditions? Running conditions, driving con\
ditions, weather conditions
w How did it happen? Problem symptoms
(Sample) Engine control system check sheet.
±
INTRODUCTION How to Troubleshoot ECU Controlled SystemsIN±17
WhereEverybodyKnowsYourName

1. CONTINUITY CHECK (OPEN CIRCUIT CHECK)(1) Disconnect the connectors at both ECU and sensor sides.
(2) Measure the resistance between the applicable terminalsof the connectors.
Resistance: 1
or less
HINT:
w Measure the resistance while lightly shaking the wire
harness vertically and horizontally.
w When tester probes are inserted into a connector, insert
the probes from the back. For waterproof connectors in
which the probes cannot be inserted from the back, be
careful not to bend the terminals when inserting the
tester probes.
2. RESISTANCE CHECK (SHORT CIRCUIT CHECK) (1) Disconnect the connectors at both ends.
(2) Measure the resistance between the applicable terminalsof the connectors and body ground. Be sure to carry out
this check on the connectors on both ends.
Resistance: 1 M
or higher
HINT: Measure the resistance while lightly shaking the wire
harness vertically and horizontally.
3. VISUAL CHECK AND CONTACT PRESSURE CHECK (a) Disconnect the connectors at both ends.
(b) Check for rust or foreign material, etc. on the terminalsof the connectors.
(c) Check crimped portions for looseness or damage and check if the terminals are secured in the lock position.
HINT: The terminals should not come out when pulled lightly.
(d) Prepare a test male terminal and insert it in the female
terminal, then pull it out.
HINT: When the test terminal is pulled out more easily than
others, there may be poor contact in that section.
IN±28
±
INTRODUCTION How to Troubleshoot ECU Controlled Systems
WhereEverybodyKnowsYourName

Actual examples of the inspection method for open circuit and short circuit ar\
e explained below.
1. OPEN CIRCUIT CHECKFor the open circuit in the wire harness in Fig. 1, perform º(a) Conti\
nuity Checkº or º(b) Voltage Checkº to
locate the section.
(a) Continuity Check
(1) Disconnect connectors (A) and (C) and measure the resistance between\
them.In the case of Fig. 2,
Between terminal 1 of connector (A) and terminal 1 of connector (C) \
±> No continuity (open)
Between terminal 2 of connector (A) and terminal 2 of connector (C) \
±> Continuity
Therefore, it is found out that there is an open circuit between terminal 1 of con\
nector (A) and terminal 1
of connector (C).
(2) Disconnect connector (B) and measure the resistance between connectors\
(A) and (B), (B) and (C).In the case of Fig. 3,
Between terminal 1 of connector (A) and terminal 1 of connector (B) \
±> Continuity
Between terminal 1 of connector (B) and terminal 1 of connector (C) \
±> No Continuity (open)
Therefore, it is found out that there is an open circuit between termina\
l 1 of connector (B) and terminal 1
of connector (C).
±
INTRODUCTION How to Troubleshoot ECU Controlled SystemsIN±29
WhereEverybodyKnowsYourName

(b) Voltage CheckIn a circuit in which voltage is applied (to the ECU connector terminal)\
, an open circuit can be checked for
by conducting a voltage check.
(1) As shown in Fig. 4, with each connector still connected, measure the voltage between\
body ground andterminal 1 of connector (A) at the ECU 5V output terminal, terminal 1 of conne\
ctor (B), and terminal
1 of connector (C), in that order.If the results are:
5 V: Between Terminal 1 of connector (A) and Body Ground
5 V: Between Terminal 1 of connector (B) and Body Ground
0 V: Between Terminal 1 of connector (C) and Body Ground
then it is f ound out that there is an open circuit in the wire harness between termi\
nal 1 of (B) and termi-
nal 1 of (C).
2. SHORT CIRCUIT CHECK If the wire harness is ground shorted as in Fig. 5, locate the section by \
conducting a ºcontinuity check with
groundº.
IN±30±
INTRODUCTION How to Troubleshoot ECU Controlled Systems
WhereEverybodyKnowsYourName