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 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

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). (Temperature
limit that no damage is done to the component).
(2) Do not apply heat directly to parts in the ECU.
HEAT METHOD: When the problem seems to occur when the suspect area is heated
WATER SPRINKLING METHOD: When the malfunction seems to occur on a rainy
day or in a high±humidity condition.
OTHER: When a malfunction seems to occur when electrical load is excessive.
Sprinkle water onto the vehicle and check to see if the
malfunction occurs.
NOTICE:
(1) Never sprinkle water directly into the engine compart-
ment, but indirectly change the temperature and humidity
by applying water spray onto the radiator front surface.
(2) Never apply water directly onto the electronic compo-
nents.
(Service hint)
If a vehicle is subject to water leakage, the leaked water may
contaminate the ECU. When testing a vehicle with a water leak-
age problem, special caution must be used.
Turn on all electrical loads including th3e heater blower,
head lights, rear window defogger, etc. and check to see
if the malfunction occurs.
± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMSIN±25

[4] DIAGNOSTIC TROUBLE CODE CHART
The inspection procedure is shown in the table below. This table permits efficient and accurate troubleshooting
using the diagnostic trouble codes displayed in the diagnostic trouble code check. Proceed with troubleshooting
in accordance with the inspection procedure given in the diagnostic chart corresponding to the diagnostic
trouble codes displayed. The engine diagnostic trouble code chart is shown below as an example.
IN±26± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS

[5] MATRIX CHART OF PROBLEM SYMPTOMS
The suspect circuits or parts for each problem symptom are shown in the table below. Use this table to trouble-
shoot the problem when a ºNormalº code is displayed in the diagnostic trouble code check but the problem is
still occurring. Numbers in the table indicate the inspection order in which the circuits or parts should be checked.
HINT: When the problem is not detected by the diagnostic system even though the problem symptom is present,
it is considered that the problem is occurring outside the detection range of the diagnostic system, or that the
problem is occurring in a system other than the diagnostic system.
± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMSIN±27

IN±28± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS

± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMSIN±29

HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION
PROCEDURE
1. For troubleshooting, diagnostic trouble code charts or problem symptom charts are provided for each
circuit with detailed 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, always confirm that the problem
symptoms are occurring, or proceed with inspection while using the symptom 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 trouble 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 connector, 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. In particular,
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 the connector. Simply
disconnecting and reconnecting the connectors once changes the condition 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
problem disappears after the check, then the cause is considered to be in the wire harness or connectors.
SHORT CIRCUIT:
This could be due to a short circuit between the wire harness and the body ground or to a short inside the switch,
etc.
HINT:
wWhen there is a short between the wire harness and body ground, check thoroughly whether the wire
harness is caught in the body or is clamped properly. IN±30
± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS

1. CONTINUITY CHECK (OPEN CIRCUIT CHECK)
(1) Disconnect the connectors at both ECU and sensor sides.
(2) Measure the resistance between the applicable terminals of
the connectors.
Resistance: 1
or less
HINT:
wMeasure the resistance while lightly shaking the wire
harness vertically and horizontally.
wWhen 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 terminals of
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 terminals of 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.
± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMSIN±31

Actual examples of the inspection method for open circuit and short circuit are explained below.
1. OPEN CIRCUIT CHECK
For the open circuit in the wire harness in Fig. 1, perform º(a) Continuity 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 connector (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 terminal 1 of connector (B) and terminal 1
of connector (C).
IN±32± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS

(b) Voltage Check
In 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
and terminal 1 of connector (A) at the ECU 5V output terminal, terminal 1 of connector (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 found out that there is an open circuit in the wire harness between terminal 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.
± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMSIN±33