1991 LEXUS SC400 Service Repair Manual

airbag off coolant temperature tow bar recommended oil tow wheel bolt torque

Page 17 of 4087

LEXUS SC400 1991 Service Repair Manual
INSPECTION AND ADJUSTMENT OF
JOINT ANGLE DURING REMOVAL
AND INSTALLATION OF
PROPELLER SHAFT
When performing operations which involve the removal and instal-
lation of the propeller shaft be sure to c

Page 18 of 4087

$LEXUS SC400 1991 Service Repair Manual HOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS A large number of ECU controlled systems are used in the LEXUS SC400. In \ general, the ECU controlled sys- tem is considered to be a very intricate system$

Page 19 of 4087

$LEXUS SC400 1991 Service Repair Manual HOW TO PROCEED WITH TROUBLESHOOTING Carry out troubleshooting in accordance with the procedure on the follow\ ing page. Here, only the basic proce- dure is shown. Details are provided in each section$

Page 20 of 4087

$LEXUS SC400 1991 Service Repair Manual [1] CUSTOMER PROBLEM ANALYSIS In troubleshooting, the problem symptoms must be confirmed accurately and \ all preconceptions must be cleared away in order to give an accurate judgment. To ascertain j$

Page 21 of 4087

$LEXUS SC400 1991 Service Repair Manual [2] SYMPTOM CONFIRMATION AND DIAGNOSTIC CODE CHECK The diagnostic system in the LEXUS SC400 fulfills various functions. The fi\ rst function is the Diagnostic Code Check in which a malfunction in the$

[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
IN±18±
INTRODUCTION How to Troubleshoot ECU Controlled Systems
WhereEverybodyKnowsYourName

Page 22 of 4087

$LEXUS SC400 1991 Service Repair Manual Taking into account the above points, a flow chart showing how to proceed with\ troubleshooting using the diag- nostic code check is shown below. This flow chart shows how to utilize the diagnostic$

Page 23 of 4087

$LEXUS SC400 1991 Service Repair Manual [3] SYMPTOM SIMULATION The most difficult case in troubleshooting is when there are no problem symptoms occurring. In s\ uch cases, a thorough customer problem analysis must be carried out, then sim$

[3] SYMPTOM SIMULATION
The most difficult case in troubleshooting is when there are no problem symptoms occurring. In s\
uch cases, a
thorough customer problem analysis must be carried out, then simulate the same or similar conditions and envi-
ronment in which the problem occurred in the customer's vehicle. No matter now much experience a technician
has, or how skilled he may be, if he proceeds to troubleshoot without confir\
ming the problem symptoms he will
tend to overlook something important in the repair operation and make a wron\
g guess somewhere, which will
only lead to a standstill. For example, for a problem which only occurs when\
the engine is cold, or for a problem
which occurs due to vibration caused by the road during driving, etc., the pr\
oblem can never be determined so
long as the symptoms are confirmed with the engine hot condition or the \
vehicle at a standstill. Since vibration,
heat or water penetration (moisture) are likely causes for problems which are \
difficult to reproduce, the symptom
simulation tests introduced here are effective measures in that the external causes are applied to the vehicle
in a stopped condition.
Important Points in the Symptom Simulation Test
In the symptom simulation test, the problem symptoms should of course be co\
nfirmed, but the problem area
or parts must also be found out. To do this, narrow down the possible problem circuits according to the sym\
ptoms
before starting this test and connect a tester beforehand. After that, carry out the symptom simulation test, judg-
ing whether the circuit being tested is defective or normal and also confir\
ming the problem symptoms at the
same time. Refer to the matrix chart of problem symptoms for each system to \
narrow down the possible causes
of the symptom.
[1] VIBRATION METHOD: When vibration seems to be the major cause.
CONNECTORS
Slightly shake the connector vertically and horizon-
tally.
WIRE HARNESS
Slightly shake the wire harness vertically and horizontally.
The connector joint, fulcrum of the vibration, and body
through portion are the major areas to be checked thor-
oughly.
PARTS AND SENSORS
Apply slight vibration with a finger to the part of the
sensor considered to be the problem cause and
check if the malfunction occurs.
HINT: Applying strong vibration to relays may result
in open relays. IN±20
±
INTRODUCTION How to Troubleshoot ECU Controlled Systems
WhereEverybodyKnowsYourName

Page 24 of 4087

LEXUS SC400 1991 Service Repair Manual
[2] HEAT METHOD: When the problem seems to occur when the suspect area is heated.
Heat the component that is the likely cause of the malfunc-
tion with a hair dryer or similar object. Check to see if

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