Lexus RX300 (MCU15). Manual - part 225

A06105
A02330

A10581

ON

FC

DI–132

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

OBD scan tool (excluding hand–held tester):

1

Check operation of fuel pump.

PREPARATION:
(a)

Remove the engine ECU with connector still connected
(See page FI–70).

(b)

Turn the ignition switch ON.

CHECK:
(a)

Connect between terminal FC of the engine ECU connec-
tor and body ground.

(b)

Check that the pulsation damper screw rises up when
connecting between terminal FC of the engine ECU con-
nector and body ground.

OK:

The pulsation damper screw rises up.

OK

Check for starter signal circuit 
(See page DI–134).

NG

2

Check for engine ECU power source circuit (See page DI–124).

NG

Repair or replace.

OK

3

Check circuit opening relay (Marking: CIR OPN) (See page FI–57).

NG

Replace circuit opening relay.

OK

A02064

ON

FC

(+)

(–)

–

DIAGNOSTICS

ENGINE

DI–133

LEXUS RX300   (RM785E)

4

Check voltage between terminal FC of engine ECU connector and body ground.

PREPARATION:
(a)

Remove the engine ECU with connector still connected
(See page FI–70).

(b)

Turn the ignition switch ON.

CHECK:
Measure the voltage between terminal FC of the engine ECU
connector and body ground.
OK:

Voltage: 9 – 14 V

OK

Go to step 5

NG

Check for open in harness and connector between EFI main relay (Marking: EFI) and circuit open-
ing relay, and circuit opening relay and engine ECU.

5

Check fuel pump (See page FI–5).

NG

Repair or replace fuel pump.

OK

6

Check for open in harness and connector between circuit opening relay and fuel
pump, and fuel pump and body ground (See page IN–32).

NG

Repair or replace harness or connector.

OK

Check and replace engine ECU 
(See page IN–32).

A05621

From Ignition
Switch

Instrument 
Panel J/B

ST

AR

TER

From Battery

Engine Room J/B

MAIN

B–W

W–B

Starter

9

9

B

1

2

3

2

1

6

5

6

9

4

1

1

B

1G

1C

IH1

2A

2I

2D

2D

S2

IE

E9

STARTER Relay

E1

STA

A

J5

7

IH1

19

J/C

1

2

Neutral Start 
Switch

B

Engine ECU

B–W

B–W

DI–134

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

Starter Signal Circuit

CIRCUIT DESCRIPTION

When the engine is cranked, the intake air flow is slow, so fuel vaporization is poor. A rich mixture is therefore
necessary in order to achieve good startability. While the engine is being cranked, the battery positive volt-
age is applied to terminal STA of the engine ECU. The starter signal is mainly used to increase the fuel injec-
tion volume for the starting injection control and after–start injection control.

WIRING DIAGRAM

INSPECTION PROCEDURE

HINT:
This diagnostic chart is based on the premise that the engine is cranked normally. If the engine is not
cranked, proceed to the problem symptoms table on page DI–21.

DI0A7–07

A02045

START

STA

(+)

(–)

–

DIAGNOSTICS

ENGINE

DI–135

LEXUS RX300   (RM785E)

Hand–held tester:

1

Connect hand–held tester, and check STA signal.

PREPARATION:
(a)

Connect the hand–held tester to the DLC3.

(b)

Turn the ignition switch ON and push the hand–held tester main switch ON.

CHECK:
Read the STA signal on the hand–held tester while the starter operates.
OK:

Ignition Switch Position

ON

START

STA Signal

OFF

ON

OK

Proceed to next circuit inspection shown on
problem symptom table (See page DI–21).

NG

2

Check for open in harness and connector between engine ECU and starter relay
(See page IN–32).

NG

Repair or replace harness or connector.

OK

Check and replace engine ECU 
(See page IN–32).

OBD scan tool (excluding hand–held tester):

1

Check voltage between terminal STA of engine ECU connector and body ground.

PREPARATION:
Remove the engine ECU with connector still connected (See
page FI–70).
CHECK:
Measure the voltage between terminal STA of the engine ECU
connector and body ground during the engine cranking.
OK:

Voltage: 6 V or more

OK

Proceed to next circuit inspection shown on
problem symptom table (See page DI–21).