Lexus RX300 (MCU15). Manual - part 80

V08425

LOCK

KNK

E6 Connector

(a) Remove the glove compartment (See page FI–68).
(b) Disconnect the E6 connector of ECM.

INSPECTION PROCEDURE

Replace knock sensor.

1

Check continuity between terminal KNK of ECM connector and body ground.

OK:

Check knock sensor (See page FI–61).

Measure resistance between terminal KNK of ECM connector 
and body ground.

Resistance: 1 MΩ or higher

Connector being checked is connected.

D Indicates the condition of the connector of ECU during the check.

PREPARATION:

CHECK:

2

Go to step 3.

OK

OK

NG

D Indicates the position of the ignition switch during the check.

Check from the connector back side.
(with harness)

Ignition Switch LOCK (OFF)

Ignition Switch START

LOCK

Ignition Switch ON

Ignition Switch ACC

START

ON

ACC

D

D Indicates the place to check the voltage or resistance.
D Indicates the connector position to checked, from the front or back side.

Connector being checked is disconnected.

Check from the connector front side. (without harness)
In this case, care must be taken not to bend the terminals.

E6 Connector

KNK

Wire Harness

E6 Connector

KNK

A00255

AB0117
A00265

Inspection Procedure
Use the inspection procedure to determine if
the circuit is normal or abnormal, and, if it is
abnormal, use it to determine whether the
problem is located in the sensors, actuators,
wire harness or ECU.

–

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

IN–31

LEXUS RX300   (RM785E)

FI0048

FI0047

FI0046

IN05X–15

IN–32

–

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

LEXUS RX300   (RM785E)

HOW TO USE THE DIAGNOSTIC
CHART AND INSPECTION
PROCEDURE

1.

CONNECTOR CONNECTION AND TERMINAL IN-
SPECTION

S

For troubleshooting, diagnostic trouble code charts or
problem symptom table are provided for each circuit with
detailed inspection procedures on the following pages.

S

When all the component parts, wire harnesses and con-
nectors of each circuit except the ECU are found to be
normal in troubleshooting, then it is determined that the
problem is in the ECU. Accordingly, if diagnosis is per-
formed without the problem symptoms occurring, refer to
Step 8 to replace the ECU. So always confirm that the
problem symptoms are occurring, or proceed with inspec-
tion while using the symptom simulation method.

S

The instructions ”Check wire harness and connector” and
”Check and replace ECU” which appear in the inspection
procedure, are common and applicable to all diagnostic
trouble codes. Follow the procedure outlined below
whenever these instructions appear.

OPEN CIRCUIT:
This could be due to a disconnected wire harness, faulty con-
tact in the connector, and a connector terminal pulled out, etc.
HINT:

S

It is rarely the case that a wire is broken in the middle of
it. Most cases occur at the connector. In particular, care-
fully check the connectors of sensors and actuators

S

Faulty contact could be due to rusting of the connector
terminals, to foreign materials entering terminals or a de-
formation of connector terminals. Simply disconnecting
and reconnecting the connectors once changes the
condition of the connection and may result in a return to
normal operation. Therefore, in troubleshooting, if no ab-
normality is found in the wire harness and connector
check, but the problem disappears after the check, then
the cause is considered to be in the wire harness or con-
nectors.

SHORT CIRCUIT:
This could be due to a contact between wire harness and the
body ground or to a short circuit occurred inside the switch, etc.
HINT:
When there is a short circuit between the wire harness and body
ground, check thoroughly whether the wire harness is caught
in the body or is clamped properly.

FI7187

IN0379

Sensor Side

ECU Side

IN0378

Sensor Side

ECU Side

IN0380

Sensor Side

ECU Side

IN0381

Pull Lightly

Looseness of Crimping

–

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

IN–33

LEXUS RX300   (RM785E)

2.

CONNECTOR HANDLING

When inserting tester probes into a connector, insert them from
the rear of the connector. When necessary, use mini test leads.
For water resistant connectors which cannot be accessed from
behind, take good care not to deform the connector terminals.

3.

CONTINUITY CHECK (OPEN CIRCUIT CHECK)

(a)

Disconnect the connectors at both ECU and sensor
sides.

(b)

Measure the resistance between the applicable terminals
of the connectors.
Resistance: 1 Ω or less

HINT:
Measure the resistance while lightly shaking the wire harness
vertically and horizontally.

4.

RESISTANCE CHECK (SHORT CIRCUIT CHECK)

(a)

Disconnect the connectors on both ends.

(b)

Measure the resistance between the applicable terminals
of the connectors and body ground. Be sure to carry out
this check on the connectors on both ends.
Resistance: 1 MΩ or higher

HINT:
Measure the resistance while lightly shaking the wire harness
vertically and horizontally.

5.

VISUAL CHECK AND CONTACT PRESSURE CHECK

(a)

Disconnect the connectors at both ends.

(b)

Check for rust or foreign material, etc. in the terminals of
the connectors.

(c)

Check crimped portions for looseness or damage and
check that the terminals are secured in lock portion.

HINT:
The terminals should not come out when pulled lightly from the
back.

Z17004

Fig. 1

OPEN

ECU

2

Sensor

2

2

2

1

1

1

1

A

B

C

Z17005

Fig. 2

ECU

Sensor

2

1

A

B

C

1

1

2

2

B04722

Fig. 3

ECU

Sensor

2

1

A

B1

C

1

1

2

2

1

2

B2

IN–34

–

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED 
SYSTEMS

LEXUS RX300   (RM785E)

(d)

Prepare a test male terminal and insert it in the female ter-
minal, then pull it out.

NOTICE:
When testing a gold–plated female terminal, always use a
gold–plated male terminal.
HINT:
When the test terminal is pulled out more easily than others,
there may be poor contact in that section.

6.

CHECK OPEN CIRCUIT

For the open circuit in the wire harness in Fig. 1, perform ”(a)
Continuity Check” or ”(b) Voltage Check” to locate the section.

(a)

Check the continuity.
(1)

Disconnect connectors ”A” and ”C” and measure
the resistance between them.
In the case of Fig. 2:
Between terminal 1 of connector ”A” and terminal 1
of connector ”C” → No continuity (open)
Between terminal 2 of connector ”A” and terminal 2
of connector ”C” → Continuity
Therefore, it is found out that there is an open circuit
between terminal 1 of connector ”A” and terminal 1
of connector ”C”.

(2)

Disconnect connector ”B” and measure the resis-
tance between the connectors.
In the case of Fig. 3:
Between terminal 1 of connector ”A” and terminal 1
of connector ”B1” → Continuity
Between terminal 1 of connector ”B2” and terminal
1 of connector ”C” → No continuity (open)
Therefore, it is found out that there is an open circuit
between terminal 1 of connector ”B2” and terminal
1 of connector ”C”.