Lexus ES300 (2002 year). Service manual - part 277

01-24

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS

2002 LEXUS ES300 REPAIR MANUAL (RM911U)

SYMPTOM CONFIRMATION AND DIAGNOSTIC TROUBLE CODE

HINT:

The diagnostic system in LEXUS ES300 has various functions. The first function is the Diagnostic
Trouble Code (DTC) Check in which a malfunction in the signal circuits to the ECU is stored in code
form in the ECU memory. 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, possible areas of the
problem can be narrowed down quickly and troubleshooting can be performed effectively. Diagnostic
functions are incorporated in the following systems in LEXUS ES300.

System

Diagnostic Trouble

Code Check

Input Signal Check

(Sensor Check)

Diagnostic Test

Mode (Active Test)

SFI System

(with Check Mode)

Electronic Modulated Suspension System

ABS with EBD System

ABS with EBD & BA & TRAC & VSC System

Electronic Controlled Automatic Transmission [ECT]

(with Check Mode)

Air Conditioning System

Supplement Restraint System

Power Window Control System

Power Door Lock Control System

Wireless Door Lock Control System

Engine Immobiliser System

Multiplex Communication System

Cruise Control System

In the DTC check, it is very important to determine whether the problem indicated by the DTC is still
occurring or has 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 DTC is directly related to the
problem symptom or not. For this reason, the DTC should be checked before and after the symptom
confirmation to determine the current conditions. If this is not done, it may, depending on the case,
result in an unnecessary troubleshooting for normally operating systems, making it more difficult to de-
tect the problem area, or trying to repair irrelevant areas. Therefore always follow the procedure in the
correct order and perform the DTC check.

A flow chart showing how to proceed with the troubleshooting using the diagnostic trouble code (DTC)
check is shown below. This flow chart shows how to utilize the DTC check effectively. Then, by carefully
checking the results, indicates how to proceed either to the DTC troubleshooting or to the troubleshoot-
ing of problem symptoms table.

DTC check

Making a note and clearing of the DTCs displayed

Symptom confirmation

Problem symptoms exist

No problem symptoms exist

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS

01-25

2002 LEXUS ES300 REPAIR MANUAL (RM911U)

Go to step 5

Simulation test using the symptom simulation methods

DTC check

DTC displayed

Normal code displayed

Troubleshooting of problem indicated by DTC

Symptom confirmation

No problem symptoms exist

Problem symptoms exist

If a DTC is displayed in the initial DTC check, it indicates that
a trouble may have occurred in a wire harness or connector in
that circuit in the past, therefore check the wire harness and
connectors (See page

01-31

System normal

Troubleshooting of each problem symptom

The problem is still occurring in a place other than the diagnostic circuit (The DTC displayed first is either
for a past problem or it is a secondary problem).

D25083

Vibrate Slightly

Shake Slightly

Vibrate
Slightly

D25084

Malfunction

01-26

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS

2002 LEXUS ES300 REPAIR MANUAL (RM911U)

SYMPTOM SIMULATION

HINT:
The most difficult case in troubleshooting is when no problem symptoms occurs. In such cases, a thorough
customer problem analysis must be carried out. Then simulate the same or similar conditions and environ-
ment 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 with the engine hot condition or the vehicle at a standstill. Since vibration, heat or water penetra-
tion (moisture) is a likely cause for the problem which is difficult to reproduce, the symptom simulation tests
introduced here are effective measures in a point that the external causes are applied to the vehicle in a
stationary condition.
Important points in the symptom simulation test:
In the symptom simulation test, the problem symptoms should be confirmed, and the problem area or parts
must also be found out. To do so, narrow down the possible problem circuits according to the symptoms
before starting this test and have a hand-held tester connected beforehand. After that, carry out the symp-
tom simulation test, judging whether the circuit being tested is defective or normal and also confirming the
problem symptoms at the same time. Refer to the problem symptoms table of each system to narrow down
the possible causes of the symptom.

VIBRATION METHOD: When vibration seems to be
the major cause.

(a)

PART AND SENSOR
(1)

Apply slight vibration with a finger to the part of the
sensor considered to be the problem cause and
check that the malfunction occurs.

HINT:
Applying strong vibration to relays may result in open relays.
(b)

CONNECTORS
(1)

Slightly shake the connector vertically and horizon-
tally.

(c)

WIRE HARNESS
(1)

Slightly shake the wire harness vertically and hori-
zontally.
The connector joint and fulcrum of the vibration are
the major areas to be checked thoroughly.

HEAT METHOD: When the problem seems to occur
when the suspect area is heated.

(a)

Heat the component that is the possible cause of the mal-
function with a hair dryer or similar object. Check if the
malfunction occurs.

NOTICE:

Do not heat to more than 60

C (140

F) (Temperature

is limited so as not to damage the components).

Do not apply heat directly to the parts in the ECU.

D25085

B02389

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS

01-27

2002 LEXUS ES300 REPAIR MANUAL (RM911U)

WATER SPRINKLING METHOD: When the malfunc-
tion seems to occur on a rainy day or in a high-humid-
ity condition.

(a)

Sprinkle water onto the vehicle and check if the malfunc-
tion occurs.

NOTICE:

Never sprinkle water directly onto the engine
compartment, but indirectly change the temperature
and humidity by applying water spray onto the radia-
tor front surface.

Never apply water directly onto the electronic compo-
nents.

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 taken.

OTHERS: When the malfunction seems to occur
when electrical load is excessive.

(a)

Turn on all the electrical loads including the heater blower,
headlights, rear window defogger, etc., and check if the
malfunction occurs.

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