Lexus RX300 (MCU15). Manual - part 79

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:

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INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

IN–27

LEXUS RX300   (RM785E)

D DTC No.
   Indicates the diagnostic trouble code.
D Page or Instructions
   Indicates the page where the inspection procedure
   for each circuit is to be found, or gives instructions
   for checking and repairs.

D Detection Item
   Indicates the system of the problem or
   contents of the problem.

D Trouble Area
   Indicates the suspect area of the 
   problem.

Mass Air Flow Circuit Malfunction

Detection Item

D Open or short in mass air flow meter circuit
D Mass air flow meter

D ECM

DTC No.

(See page)

Trouble Area

MIL*

Memory

P0100

(DI–24)

P0101

(DI–28)

P0115

(DI–33)

D Open or short in intake air temp. sensor 

   circuit

D Intake air temp. sensor
D ECM

Intake Air Temp. Circuit 

Malfunction

P0110

(DI–29)

D Open or short in engine coolant temp. sensor circuit
D Engine coolant temp. sensor

D ECM

Throttle/ Pedal Position Sensor/Switch

”A” Circuit Malfunction

Engine Coolant Temp. 

Circuit Malfunction

D Open or short in throttle position sensor circuit
D Throttle position sensor

D ECM

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.

Mass Air Flow Circuit

Range/ Performance Problem

D Mass air flow meter

D Throttle position sensor

Throttle/ Pedal Position Sensor/ Switch

”A” Circuit Range / Performance Prob-

lem

P0116

(DI–37)

Engine Coolant Temp. 

Circuit Range/ Performance Problem

D Engine coolant temp. sensor
D Cooling system

IN–28

–

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

LEXUS RX300   (RM785E)

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.

–

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

IN–29

LEXUS RX300   (RM785E)

5.

PROBLEM SYMPTOMS TABLE

The suspected circuits or parts for each problem symptom are shown in the table below. Use this table to
troubleshoot the problem when a ”Normal” code is displayed in the diagnostic trouble code check but the
problem is still occurring. Numbers in the table indicate the inspection order in which the circuits or parts
should be checked.
HINT:
When the problem is not detected by the diagnostic system even though the problem symptom is present,
it is considered that the problem is occurring outside the detection range of the diagnostic system, or that
the problem is occurring in a system other than the diagnostic system.

Symptom

Suspect Area

See page

Engine does not crank (Does not start)

No initial combustion (Does not start)

No complete combustion (Does not start)

1. Starter and starter relay

1. ECM power source circuit

2. Fuel pump control circuit

3. Engine control module (ECM)

1. Starter signal circuit

2. Fuel pump control circuit

1. Fuel pump control circuit

DI–147

DI–151

IN–29

PROBLEM SYMPTOMS TABLE

1. Compression

2. Fuel pump control circuit

1. A/C signal circuit

2. Fuel pump control circuit

1. A/C signal circuit (Compressor circuit)

2. ECM power source circuit

1. Starter signal circuit

2. Fuel pump control circuit

1. Starter signal circuit

2. Fuel pump control circuit

3. Compression

idling)

High engine idle speed (Poor idling)

Hot engine

Cold engine (Difficult to start)

Engine cranks normally (Difficult to start)

AC–88

DI–144

DI–151

EM–3

DI–151

D Problem Symptom

D Page 
   Indicates the page where the flow chart for each circuit 
   is located.

D Circuit Inspection, Inspection Order
   Indicates the circuit which needs to be checked for each problem 
   symptom. Check in the order indicated by the numbers.

D Circuit or Part Name
   Indicates the circuit or part which needs to be checked.

ST–2
ST–17

DI–144

DI–151

DI–144

DI–151

V08423

Knock Sensor 1

GR

ECM

KNK

E1

12
E6

WIRING DIAGRAM

Wiring Diagram
This shows a wiring diagram of the circuit.
Use this diagram together with ELECTRICAL
WIRING DIAGRAM to thoroughly understand the
circuit.
Wire colors are indicated by an alphabetical code.
B = Black, L = Blue, R = Red, BR = Brown,
LG = Light Green, V = Violet, G = Green,
O = Orange, W = White, GR = Gray, P = Pink,
Y = Yellow, SB = Sky Blue
The first letter indicates the basic wire color and
the second letter indicates the color of the stripe.

DTC

P0325

Knock Sensor 1 Circuit Malfunction

CIRCUIT DESCRIPTION

Knock sensor is fitted to the cylinder block to detect engine knocking. This sensor contains a piezoelectric element which

generates a voltage when it becomes deformed, which occurs when the cylinder block vibrates due to knocking. If engine

knocking  occurs, ignition timing is retarded to suppress it.

DTC No.

DTC Detecting Condition

Trouble Area

P0325

No knock sensor 1 signal to ECM with engine speed, 

1,200 rpm or more.

D Open or short in knock sensor1 circuit

D Knock sensor 1 (looseness)

D ECM

If the ECM detects the above diagnosis conditions, it operates the fall safe function in which the corrective retard angle

value is set to the maximum value.

D Diagnostic Trouble Code No. and Detection Item

D Circuit Description
   The major role and operation, etc. of the circuit 
   and its component parts are explained.

D Indicates the diagnostic trouble code, diagnostic 
   trouble code set parameter and suspect area of 
   the problem.

D

IN–30

–

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

LEXUS RX300   (RM785E)

6.

CIRCUIT INSPECTION

How to read and use each page is shown below.