Lexus GS300/400 (2000 year). Manual — part 157

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–23

23

2.

SYMPTOM CONFIRMATION AND DIAGNOSTIC TROUBLE CODE CHECK

The diagnostic system in the LEXUS GS400/GS300 fulfills various functions. The first function is the Diag-
nostic 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 func-
tion 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
GS400/GS300.

System

Diagnostic Trouble

Code Check

Input Signal Check

(Sensor Check)

Diagnostic Test

Mode (Active Test)

Engine (2JZ–GE)

Engine (1UZ–FE)

Automatic Transmission

ABS & Hydraulic Brake Booster Power Supply System

Vehicle Skid Control (VSC) & Brake Assist (BA) System

Power Tilt and Power Telescopic Steering Column

Supplemental Restraint System

Cruise Control System

Engine Immobiliser System

Multiplex Communication System

LEXUS Navigation System

Air Conditioning System

(with check Mode)

(with check Mode)

(with check 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.

Diagnostic trouble code check

Making a note of and clearing of the diagnostic trouble codes displayed

Symptom confirmation

No problem symptoms
exist

Problem symptoms
exist

Simulation test using the symptom
simulation methods

Normal code displayed

Problem symptoms exist

Normal code displayed

No problem symptoms exist

Diagnostic trouble code check

Troubleshooting of problem indicated
by diagnostic trouble code

Diagnostic trouble code displayed

Problem symptoms exist

System Normal

Troubleshooting of each
problem symptom

If a diagnostic trouble code was
displayed in the initial diagnostic
trouble code check, it indicates
that the trouble may have occurred
in a wire harness or connector in
that circuit in the past. Therefore,
check the wire harness and con-
nectors (See page

IN–31

).

IN–24

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INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS

24

Taking into account the points on the previous page, a flow chart showing how to proceed with troubleshoot-
ing using the diagnostic trouble code check is shown below. This flow chart shows how to utilize the diagnos-
tic trouble code check effectively, then by carefully checking the results, indicates how to proceed either to
diagnostic trouble code troubleshooting or to troubleshooting of problem symptoms table.

V07268

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

CONNECTORS

WIRE HARNESS

PARTS AND SENSOR

1

Slightly shake the connector vertically and horizontally.

Slightly shake the wire harness vertically and horizontally.
The connector joint, fulcrum of the vibration, and body
through portion are the major areas to be checked thorough-
ly.

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

Shake Slightly

Swing Slightly

Vibrate Slightly

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

–

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS

IN–25

25

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
environment 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 en-
gine is cold, or for a problem which occurs due to vibration caused by the road during driving, etc., the prob-
lem 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) is likely cause for problem which
is difficult to reproduce, the symptom simulation tests introduced here are effective measures in that the ex-
ternal 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 symp-
toms before starting this test and connect a tester beforehand. After that, carry out the symptom simulation
test, judging whether the circuit being tested is defective or normal and also confirming the problem symp-
toms at the same time. Refer to the problem symptoms table for each system to narrow down the possible
causes of the symptom.

B02389

B02390

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

2

NOTICE:

3

WATER SPRINKLING METHOD:

(1)

(2)

4

OTHER: When a malfunction seems to occur when electrical load is excessive.

When the malfunction seems to occur on a rainy day or in a
high–humidity condition.

Heat the component that is the likely cause of the malfunction
with a hair dryer or similar object. Check to see if the malfunction
occurs.

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

Turn on all electrical loads including the heater blower, head
lights, rear window defogger, etc. and check to see if the mal-
function occurs.

ON

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.

M a l f u n c-

tion

Do not heat to more than 60

°

C (140

°

F). (Temperature

is limited not to damage the components.)
Do not apply heat directly to parts in the ECU.

(1)

(2)

Never sprinkle water directly into the engine compart-
ment, but indirectly change the temperature and hu-
midity by applying water spray onto the radiator front
surface.
Never apply water directly onto the electronic compo-
nents.

NOTICE:

IN–26

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INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS

26