Lexus ES300 (1997 year). Manual - part 489

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–27

).

IN–20

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INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

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1997 LEXUS ES300   (RM511U)

Taking into account the above points, a flow chart showing how to proceed with troubleshooting using the
diagnostic trouble code check is shown below. This flow chart shows how to utilize the diagnostic 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.

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 
malfunction occurs.

Shake Slightly

Swing Slightly

Vibrate Slightly

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

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INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

IN–21

21

1997 LEXUS ES300   (RM511U)

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 matrix chart of problem symptoms for each system to narrow down the
possible causes of the symptom.

V07469

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

2

NOTICE:
(1) Do not heat to more than 60 

°

C (140 

°

F). (Temperature

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

3

WATER SPRINKLING METHOD:

NOTICE:
(1) Never sprinkle water directly into the engine
    compartment, but indirectly change the temperature and
    humidity by applying water spray onto the radiator front
    surface.
(2) Never apply water directly onto the electronic
    components.

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

(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 taken.

M a l f u n c-
tion

IN–22

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HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

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1997 LEXUS ES300   (RM511U)

 DTC No.

   Indicates the diagnostic trouble code.

 Page or Instructions

   Indicates the page where the inspection procedure
   for each circuit is to be found, or gives instructions
   for checking and repairs.

 Detection Item

   Indicates the system of the problem or
   contents of the problem.

 Trouble Area

   Indicates the suspect area of the 
   problem.

Mass Air Flow Circuit Malfunction

Detection Item

 Open or short in mass air flow meter circuit

 Mass air flow meter

 ECM

DTC No.

(See page)

Trouble Area

MIL*

Memory

P0100

(DI–26)

P0101

(DI–31)

Mass Air Flow Circuit 

Range/Performance Problem

 Mass air flow meter

P0115

(DI–37)

 Open or short in intake air temp. sensor circuit

 Intake air temp. sensor

 ECM

Intake Air Temp. Circuit Malfunction

P0110

(DI–32)

Engine Coolant Temp. Circuit 

Range/Performance Problem

 Open or short in engine coolant temp. sensor circuit

 Engine coolant temp. sensor

 ECM

P0120

(DI–43)

Throttle/ Pedal Position Sensor/Switch

”A” Circuit Range/Performance

P0116

(DI–41)

Throttle/Pedal Position Sensor/Switch

”A” Circuit Malfunction

Insufficient Coolant Temp. for Closed

 Engine coolant temp. sensor

 Cooling system

Engine Coolant Temp. Circuit 

Malfunction

 Open or short in throttle position sensor circuit

 Throttle position sensor

 ECM

 Throttle position sensor

 Open or short in heated oxygen sensor circuit

 Heated oxygen sensor

DTC CHART (SAE Controlled)

HINT:
Parameters listed in the chart may not be exactly the same as your reading due to the type of instrument or other
factors.

If a malfunction code is displayed during the DTC check mode, check the circuit for that code listed in the table
below. For details of each code, turn to the page referred to under the ”See page” for the respective ”DTC No.”
in the DTC chart.

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INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

IN–23

23

1997 LEXUS ES300   (RM511U)

4.

DIAGNOSTIC TROUBLE CODE CHART

The inspection procedure is shown in the table below. This table permits efficient and accurate troubleshoot-
ing using the diagnostic trouble codes displayed in the diagnostic trouble code check. Proceed with trouble-
shooting 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.