Lexus RX300 (MCU15). Manual — part 223
A14522
Switch
Instrument Panel J/B
B
W–R
B–O
W–L(*1)
IGN
1
6
3
12
1C
1C
7
6
1G
2C
2B
2B
2B
2I 1
6
5
4
5
1
2
3
5
EFI
EFI
Relay
W
1
3
F11
FL Block
W
Battery
EC
Engine ECU
J/C
A
A
J4
E9
17
16
E7
A
J10
E1
Engine Room
J/B
B–W
2
8
IGSW
MREL
B+
1G
J2
J/C
ED
E9
E9
I15 Ignition
BR
A
J/C
A
BR
W–R(*2)
(*1): LHD
(*2): RHD
W–B
B–R
B–R
AM2
DI–124
–
DIAGNOSTICS
ENGINE
LEXUS RX300 (RM785E)
ECU Power Source Circuit
CIRCUIT DESCRIPTION
When the ignition switch is turned ON, battery positive voltage is applied to terminal IGSW of the engine ECU
and the EFI main relay (Marking: EFI) control circuit in the engine ECU sends a signal to terminal MREL of
the engine ECU switching on the EFI main relay.
This signal causes current to flow to the coil, closing the contacts of the EFI main relay and supplying power
to terminal +B of the engine ECU.
If the ignition switch is turned off, the engine ECU continues to switch on the EFI main relay for a maximum
of 2 seconds for the initial setting of the IAC valve.
WIRING DIAGRAM
DI6EA–02
A02040
ON
E1
+B
(–)
(+)
A02344
ON
IGSW
(+)
(–)
–
DIAGNOSTICS
ENGINE
DI–125
LEXUS RX300 (RM785E)
INSPECTION PROCEDURE
1
Check voltage between terminals +B and E1 of engine ECU connectors.
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 terminals +B and E1 of the en-
gine ECU connectors.
OK:
Voltage: 9 – 14 V
OK
Proceed to next circuit inspection shown on
problem symptoms table (See page DI–21).
NG
2
Check for open in harness and connector between terminal E1 of engine ECU
and body ground (See page IN–32).
NG
Repair or replace harness or connector.
OK
3
Check voltage between terminal IGSW 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 IGSW of the engine
ECU connector and body ground.
OK:
Voltage: 9 – 14 V
OK
Go to step 6.
NG
F05273
A10577
Instrument Panel J/B
IGN Fuse
A02345
ON
MREL
(+)
(–)
DI–126
–
DIAGNOSTICS
ENGINE
LEXUS RX300 (RM785E)
4
Check IGN fuse.
PREPARATION:
Remove the IGN fuse from the instrument panel J/B.
CHECK:
Check the continuity of the IGN fuse.
OK:
Continuity
NG
Check for short in all harness and components
connected to IGN fuse.
OK
5
Check ignition switch (See page BE–26).
NG
Replace ignition switch.
OK
Check and repair harness and connector be-
tween battery and ignition switch, and igni-
tion switch and engine ECU.
6
Check voltage between terminal MREL of engine ECU 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 MREL of engine ECU
and body ground.
OK:
Voltage: 9 – 14 V
–
DIAGNOSTICS
ENGINE
DI–127
LEXUS RX300 (RM785E)
NG
Check and replace engine ECU
(See page IN–32).
OK
7
Check EFI fuse (See page DI–113, step 2).
NG
Check for short in all harness and components
connected to EFI fuse.
OK
8
Check EFI main relay (Marking: EFI) (See page FI–55).
NG
Replace EFI main relay.
OK
9
Check for open and short in harness and connector between terminal MREL of
engine ECU and body ground (See page IN–32).
NG
Repair or replace harness or connector.
OK
Check and repair harness or connector be-
tween EFI fuse and battery.
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