1991 LEXUS SC400 Service Repair Manual

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Page 25 of 4087

LEXUS SC400 1991 Service Repair Manual
[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 chec

Page 26 of 4087

$LEXUS SC400 1991 Service Repair Manual [5] MATRIX CHART OF PROBLEM SYMPTOMS The suspect circuits or parts for each problem symptom are shown in the tab\ le below. Use this table to trouble- shoot the problem when a ºNormalº code is disp$

Page 27 of 4087

LEXUS SC400 1991 Service Repair Manual
6 CIRCUIT INSPECTION
How to read and use each page is shown below.
IN±24±
INTRODUCTION How to Troubleshoot ECU Controlled Systems
WhereEverybodyKnowsYourName

Page 28 of 4087

$LEXUS SC400 1991 Service Repair Manual Location of Connectors in Engine Compartment wLocation of connectors This diagram shows the wire harnesses and connectors used in one system.\ The connector shows the harness side connector, so when$

Page 29 of 4087

LEXUS SC400 1991 Service Repair Manual
IN±26±
INTRODUCTION How to Troubleshoot ECU Controlled Systems
WhereEverybodyKnowsYourName

Page 30 of 4087

$LEXUS SC400 1991 Service Repair Manual HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE 1. For troubleshooting, diagnostic code charts or problem symptom charts are p\ rovided for each circuit withdetailed inspection procedures$

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.
±
INTRODUCTION How to Troubleshoot ECU Controlled SystemsIN±27
WhereEverybodyKnowsYourName

Page 31 of 4087

LEXUS SC400 1991 Service Repair Manual
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

Page 32 of 4087

$LEXUS SC400 1991 Service Repair Manual Actual examples of the inspection method for open circuit and short circuit ar\ e explained below. 1. OPEN CIRCUIT CHECKFor the open circuit in the wire harness in Fig. 1, perform º(a) Conti\ nuity$

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