1995 TOYOTA SUPRA Service Repair Manual

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Page 1185 of 2543

TOYOTA SUPRA 1995 Service Repair Manual IF VEHICLE IS EQUIPPED WITH MOBILE
COMMUNICATION SYSTEM
For vehicles with mobile communication systems such as
two±way radios and cellular telephones, observe the follow-
ing precautions.
(1) Instal

Page 1186 of 2543

TOYOTA SUPRA 1995 Service Repair Manual HOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS
A large number of ECU controlled systems are used in the TOYOTA SUPRA. In general, the ECU controlled
system is considered to be a very intricate system requ

HOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS
A large number of ECU controlled systems are used in the TOYOTA SUPRA. In general, the ECU controlled
system is considered to be a very intricate system requiring a high level of technical knowledge and expert skill
to troubleshoot. However, the fact is that if you proceed to inspect the circuits one by one, troubleshooting of
these systems is not complex. If you have adequate understanding of the system and a basic knowledge of
electricity, accurate diagnosis and necessary repair can be performed to locate and fix the problem. This manual
is designed through emphasis of the above standpoint to help service technicians perform accurate and effec-
tive troubleshooting, and is compiled for the following major ECU controlled systems:
Repair Manual System Page

Vol 1

1
2JZ±GE Engine EG±381
Vol. 1 1. 2JZ±GTE Engine EG±487

2
A340E (2JZ±GE) Automatic Transmission AT1±31 2. A340E (2JZ±GTE) Automatic Transmission AT1±31

3.

Anti±Lock Brake

BR±51
Vol 2 4. Traction Control BR±123
Vol. 2 5. Supplemental Restraint System RS±41
6. Theft Deterrent and Door Lock System BE±142
7. Cruise Control BE±163
8. Air Conditioning AC±13
The troubleshooting procedure and how to make use of it are described on the following pages.
± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMSIN±19

Page 1187 of 2543

TOYOTA SUPRA 1995 Service Repair Manual HOW TO PROCEED WITH TROUBLESHOOTING
Carry out troubleshooting in accordance with the procedure on the following page. Here, only the basic proce-
dure is shown. Details are provided in each section, s

Page 1188 of 2543

TOYOTA SUPRA 1995 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 jus

Page 1189 of 2543

TOYOTA SUPRA 1995 Service Repair Manual [2] SYMPTOM CONFIRMATION AND DIAGNOSTIC TROUBLE CODE CHECK
The diagnostic system in the TOYOTA SUPRA fulfills various functions. The first function is the Diagnostic
Trouble Code Check in which a mal

[2] SYMPTOM CONFIRMATION AND DIAGNOSTIC TROUBLE CODE CHECK
The diagnostic system in the TOYOTA SUPRA fulfills various functions. The first function is the Diagnostic
Trouble 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. Another function is the Input
Signal Check which checks if the signals from various switches are sent to the ECU correctly. The air condition-
ing system has an Actuator Check function whereby the ECU automatically operates the actuators of the damp-
er and blowermotor, etc. to check the operation. By using these check functions, the problem areas can be nar-
rowed down quickly and troubleshooting can be performed effectively. Diagnostic functions are incorporated
in the following systems in the TOYOTA SUPRA.

System

Diagnostic Trouble
Code Check

Input Signal Check
(Sensor Check)

Other Diagnosis
Function

Engine
Automatic Transmission
Anti±Lock Brake
Traction Control (Option)
Supplemental Restraint System
Cruise Control
Air Conditioning

O (with Test Mode)
O (with Test Mode)
O
O
O
O
O

O
O
O
O
O
O

Actuator Check
In diagnostic trouble code check, it is very important to determine whether the problem indicated by the diagnos-
tic trouble code is still occurring or occurred in the past but returned to normal at present. In addition, it must
be checked in the problem symptom check whether the malfunction indicated by the diagnostic trouble code
is directly related to the problem symptom or not. For this reason, the diagnostic trouble codes should be
checked before and after the symptom confirmation to determine the current conditions, as shown in the table
below. If this is not done, it may, depending on the case, result in unnecessary troubleshooting for normally oper-
ating systems, thus making it more difficult to locate the problem, or in repairs not pertinent to the problem.
Therefore, always follow the procedure in correct order and perform the diagnostic trouble code check.
DIAGNOSTIC TROUBLE CODE CHECK PROCEDURE

Diagnostic Trouble
Code Check (Make a
note of and then clear)

Confirmation of
symptoms

Diagnostic Trouble
Code Check

Problem Condition

Diagnostic
Trouble Code
Display

Problem symptoms
exist

Same Diagnostic
trouble code is dis-
played

Problem is still occurring in the diagnos-
tic circuit

%

Normal code is dis-
played

The problem is still occurring in a place
other than in the diagnostic circuit. (The
diagnostic trouble code displayed first is
either for a past problem or it is a sec-
ondary problem.)

%

No problem
symptoms exist

The problem occurred in the diagnostic
circuit in the past.

Normal Code Display
%

Problem symptoms
exist

Normal code is dis-
played

The problem is still occurring in a place
other than in the diagnostic circuit.

%

No problem
symptoms exist

Normal code is dis-
played

The problem occurred in a place other
than in the diagnostic circuit in the past.
IN±22± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS

Page 1190 of 2543

TOYOTA SUPRA 1995 Service Repair Manual Taking into account the above points, a flow chart showing how to proceed with troubleshooting using the diag-
nostic trouble code check is shown below. This flow chart shows how to utilize the diagno

Page 1191 of 2543

TOYOTA SUPRA 1995 Service Repair Manual [3] SYMPTOM SIMULATION
The most difficult case in troubleshooting is when there are no problem symptoms occurring. In such cases, a
thorough customer problem analysis must be carried out, then simula

[3] SYMPTOM SIMULATION
The most difficult case in troubleshooting is when there are no problem symptoms occurring. In such 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 how much experience a technician
has, or how skilled he may be, if he proceeds to troubleshoot without confirming the problem symptoms he will
tend to overlook something important in the repair operation and make a wrong 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 problem 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 confirmed, but the problem area
or parts must also be found out. To do this, narrow down the possible problem circuits according to the symptoms
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 confirming 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.
VIBRATION METHOD: When vibration seems to be the major cause.
CONNECTORS
Slightly shake the connector vertically and horizontally.
WIRE HARNESS
Slightly shake the connector 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 sen-
sor considered to be the problem cause and check if the
malfunction occurs.
HINT: Applying strong vibration to relays may result in
open relays. IN±24
± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS

Page 1192 of 2543

TOYOTA SUPRA 1995 Service Repair Manual Heat the component that is the likely cause of the mal-
function with a hair dryer or similar object. Check to see
if the malfunction occurs.
NOTICE:
(1) Do not heat to more than 60°C (140°F). (Tem

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