Lexus RX300 (MCU15). 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).
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