Lexus RX300 (MCU15). Service manual - part 224

A02015

EFI

IGN

MAIN

IG Switch

AM2

Battery

EFI Main
Relay

Circuit Opening
Relay

Fuel Pump

STARTER
Relay

Starter

Neutral Start Switch

Engine ECU

FC

Tr

STA

NE

(STA Signal)

(NE Signal)

MAIN

STARTER

MREL

IG
SW

DI–128

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

Fuel Pump Control Circuit

CIRCUIT DESCRIPTION

In the diagram below, when the engine is cranked, current flows from terminal ST of the ignition switch to
the starter relay coil and also current flows to terminal STA of engine ECU (STA signal).
When the STA signal and NE signal are input to the engine ECU, Tr is turned ON, current flows to coil of
the circuit opening relay, the relay switches on, power is supplied to the fuel pump and the fuel pump oper-
ates.
While the NE signal is generated (engine running), the engine ECU keeps Tr ON (circuit opening relay ON)
and the fuel pump also keeps operating.

DI1BW–07

A14523

Engine ECU

R/B No. 1(*1) R/B No. 4(*2)

Instrument Panel J/B

I15 Ignition Switch

Engine Room J/B

Battery

FC

E9

3

L–Y

4

(*2)

(*1)

4

4

4

1

1

1

B–O

1

(*1) (*2)

1

2

3

5

B

1G

6

IGN

1C

1C

1G

12

3

1

B–W

W–R(*2)

W–L(*1)

W–R

B–R

IB1 8

B–R

F18
Fuel 
Pump

CIRCUIT OPENING Relay

4

5

B–W

MREL

E9

8

W–B

A

A

ED

W–B

J12
J/C

BI

W

2C

2B

2B

2F

2I

1

4

5

8

6

AM2

EFI

EFI Relay

1

2

5

3

F11

FL Block

1

3

W

W–B

A

J2
J/C

(*2): RHD

(*1): LHD

6

7

IG2

AM2

–

DIAGNOSTICS

ENGINE

DI–129

LEXUS RX300   (RM785E)

WIRING DIAGRAM

BE6653
A02330

A10579

DI–130

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

INSPECTION PROCEDURE
Hand–held tester:

1

Connect hand–held tester, and check operation of fuel pump.

PREPARATION:
(a)

Connect the hand–held tester to the DLC3.

(b)

Turn the ignition switch ON and push the hand–held tes-
ter main switch ON.

(c)

Use the ACTIVE TEST mode to operate the fuel pump.

CHECK:
Check that the pulsation damper screw rises up when the fuel
pump is operated by the hand–held tester.
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 (See page FI–57).

NG

Replace circuit opening relay.

OK

A02064

ON

FC

(+)

(–)

–

DIAGNOSTICS

ENGINE

DI–131

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).