Lexus ES300 (1997 year). Manual - part 488

IN026–02

IN–16

–

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

16

1997 LEXUS ES300   (RM511U)

HOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS

GENERAL INFORMATION

A large number of ECU controlled systems are used in the LEXUS ES300. 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, troubleshoot-
ing of these systems is not complex. If you have adequate understanding of the system and a basic knowl-
edge 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 ac-
curate and effective troubleshooting, and is compiled for the following major ECU controlled systems:

System

Page

1. Engine

DI–1

2. Automatic Transaxle

DI–148

3. Electronic Modulated Suspension

DI–194

4. Anti–Lock Brake System

DI–230

5. ABS & Traction Control System

DI–270

6. Supplemental Restraint System

DI–322

7. Theft Deterrent System

DI–396

8. Wireless Door Lock Control System

DI–441

9. Cruise Control System

DI–476

10. Air Conditioning System

DI–526

The troubleshooting procedure and how to make use of it are described on the following pages.
FOR USING OBD  SCAN TOOL OR LEXUS HAND–HELD TESTER

Before using the OBD  scan tool or LEXUS hand–held tester, the OBD  scan tool’s instruction book
or LEXUS hand held–tester’s operator manual should be read throughly.

If the OBD  scan tool or LEXUS hand–held tester cannot communicate with ECU controlled systems
when you have connected the cable of the OBD  scan tool or LEXUS hand–held tester to DLC3,
turned the ignition switch ON and operated the scan tool, there is a problem on the vehicle side or tool
side.
(1)

If communication is normal when the tool is connected to another vehicle, inspect the diagnosis
data link line (Bus

line) or ECU power circuit of the vehicle.

(2)

If communication is still not possible when the tool is connected to another vehicle, the problem
is probably in the tool itself, so perform the Self Test procedures outlined in the Tester Operator’s
Manual.

IN027–02

Vehicle Brought Workshop

Customer Problem
Analysis

Symptom Confirmation
and Diagnostic Trouble
Code Check

Symptom Simulation

Diagnostic Trouble 
Code Chart

Matrix Chart of Problem
Symptoms

Circuit Inspection or Parts
Inspection

Repair

Confirmation Test

End

1

2

4

3

5

6

7

8

Ask the customer about the conditions and the
environment when the problem occurred.

1

Confirm the symptoms and the problem conditions,
and check the diagnostic trouble codes.
(When the problem symptoms do not appear 
during confirmation, use the symptom simulation
method described later on.)

2, 3

Check the results obtained in Step 2, then confirm 
the inspection procedure for the system or the part
which should be checked using the diagnostic
trouble code chart or the matrix chart of problem
symptoms.

4, 5, 6

Check and repair the affected system or part in 
accordance with the instructions in Step 6.

7

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 occurred for
the first time.)

8

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INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

IN–17

17

1997 LEXUS ES300   (RM511U)

HOW TO PROCEED WITH TROUBLESHOOTING

Carry out troubleshooting in accordance with the procedure on the following page. Here, only the basic pro-
cedure 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 beginning troubleshooting of that
circuit.

Important Points in the Customer Problem Analysis

 What ––––– Vehicle model, system name

 When ––––– Date, time, occurrence frequency

 Where ––––– Road conditions

 Under what conditions? ––––– Running conditions, driving conditions, weather conditions

 How did it happen? ––––– Problem symptoms

(Sample) Engine control system check sheet.

ENGINE CONTROL SYSTEM Check Sheet

Customer’s Name

Driver’s Name

Data Vehicle
Brought in

License No.

Model and Model
Year

Frame No.

Engine Model

Odometer Reading

km
miles

Problem Symptoms

Engine does
not Start

Difficult to
Start

Poor Idling

Poor
Drive ability

Engine Stall

Others

Engine does not crank

No initial combustion

No complete combustion

Engine cranks slowly

Other

Incorrect first idle

Idling rpm is abnormal

High (                    rpm)

Low (                    rpm)

Rough idling

Other

Hesitation

Back fire

Muffler explosion (after–fire)

Surging

Knocking

Other

Soon after starting

After accelerator pedal depressed

After accelerator pedal released

During A/C operation

Shifting from N to D

Other

Datas Problem

Constant

Sometimes (          times per          day/month)

Inspector’s
Name

CUSTOMER PROBLEM ANALYSIS CHECK

IN–18

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INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

18

1997 LEXUS ES300   (RM511U)

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 judgement. To ascertain just what the problem symptoms are, it
is extremely important to ask the customer about the problem and the conditions at the time it occurred.
Important Point in the Problem Analysis:
The following 5 items are important points in the problem analysis. Past problems which are thought to be
unrelated and the repair history, etc. may also help in some cases, so as much information as possible should
be gathered and its relationship with the problem symptoms should be correctly ascertained for reference
in troubleshooting. A customer problem analysis table is provided in the troubleshooting section for each
system for your use.

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
displayed

Problem is still occurring in the diagnostic
circuit

Normal code is
displayed

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
secondary problem)

No problem 
symptoms exist

The problem occurred in the diagnostic
circuit in the past

Normal Code Display

Problem symptoms
exist

Normal code is 
displayed

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

No problem 
symptoms exist

Normal code is 
displayed

The problem occurred in a place other
than in the diagnostic circuit in the past

–

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

IN–19

19

1997 LEXUS ES300   (RM511U)

2.

SYMPTOM CONFIRMATION AND DIAGNOSTIC TROUBLE CODE CHECK

The diagnostic system in the LEXUS ES300 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.
By using these check functions, the problem areas can be narrowed down quickly and troubleshooting can
be performed effectively. Diagnostic functions are incorporated in the following systems in the LEXUS
ES300.

System

Diagnostic Trouble

Code Check

Input Signal Check

(Sensor Check)

Other Diagnosis

Function

Engine

Automatic Transmission

Anti–Lock Brake System (& Traction Control)

Supplemental Restraint System

Cruise Control



 (with Test Mode)



 (with Test Mode)













Diagnostic Test

Mode

Diagnostic Test

Mode

In diagnostic trouble code check, it is very important to determine whether the problem indicated by the diag-
nostic 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 operating 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.