Lexus RX300 (MCU15). Service manual — part 405
I08350
W–L
3
B
A/C ECU (Combina-
tion meter ECU)
C12
1K
1
1G
10
Instrument Panel J/B
W–R
2A
4
ECU–B
Short Pin
2I
1
Engine Room J/B
W
1
3
F11
Fusible Link Block
W
Battery
DI–850
–
DIAGNOSTICS
AIR CONDITIONING SYSTEM
LEXUS RX300 (RM785E)
Back Up Power Source Circuit
CIRCUIT DESCRIPTION
This is the backup poser source for the A/C ECU (Combination meter ECU). Power is supplied even when
the ignition switch is off and is used for diagnostic trouble code memory, etc.
WIRING DIAGRAM
DI3G6–03
I08349
+B
(–)
(+)
I08371
Engine Room J/B
ECU–B
–
DIAGNOSTICS
AIR CONDITIONING SYSTEM
DI–851
LEXUS RX300 (RM785E)
INSPECTION PROCEDURE
1
Check voltage between terminal +B of A/C ECU (Combination meter ECU) con-
nector and body ground.
PREPARATION:
Remove the A/C ECU (Combination meter ECU) with connec-
tor still connected.
CHECK:
Measure voltage between terminal +B of A/C ECU (Combina-
tion meter ECU) connector and body ground.
OK:
Voltage : Battery voltage
OK
Proceed to next circuit inspection shown on
problem symptoms table (See page DI–812).
NG
2
Check ECU–B fuse.
PREPARATION:
Remove ECU–B fuse from Engine Room J/B.
CHECK:
Check continuity of ECU–B fuse.
OK:
Continuity
NG
Check for short in all the harness and compo-
nents connected to the ECU–B fuse (See at-
tached wiring diagram).
OK
Check and repair harness and connector between A/C ECU (Combination meter ECU) and bat-
tery.
I08351
A/C ECU (Combina-
tion Meter ECU)
BLW
C12
4
IJ1
15*
1
4*
2
IG1
1
2
P–L
P–L
B3
1
W–B
3
J/C
B4
2
Blower Motor
Control Relay
B3
L–R
HEATER Relay
B4
1
R
B
2
1
B2 Blower Motor
IG1
W–B
IG1
2
B3
P–L
L–R
A
+B
SI
GND
M+
M–
IG*
1
IE*
2
J9*
1
J5*
2
*
1
: LHD
*
2
: RHD
3
DI–852
–
DIAGNOSTICS
AIR CONDITIONING SYSTEM
LEXUS RX300 (RM785E)
Blower Motor Circuit
CIRCUIT DESCRIPTION
This is the power source for the blower motor.
WIRING DIAGRAM
DI3G7–03
I08352
BLW(+)
(–)
I05290
1
2
LHD
RHD
–
DIAGNOSTICS
AIR CONDITIONING SYSTEM
DI–853
LEXUS RX300 (RM785E)
INSPECTION PROCEDURE
1
Check voltage between terminal BLW of A/C ECU (Combination meter ECU) con-
nector and body ground.
PREPARATION:
Remove the A/C ECU (Combination meter ECU) with connec-
tor still connected.
CHECK:
(a)
Turn ignition switch ON.
(b)
Operate blower motor.
(c)
Measure voltage between terminal BLW of A/C ECU
(Combination meter ECU) and body ground.
OK:
Voltage : 1 ± 3 V
OK
Proceed to next circuit inspection shown on
problem symptoms table (See page DI–812).
NG
2
Check blower motor.
PREPARATION:
Remove blower motor (See page AC–36).
CHECK:
Connect the positive (+) lead from the battery to terminal 2 of
blower motor connector and the negative (–) lead to terminal 1.
OK:
Blower motor operates smoothly.
NG
Replace blower motor.
OK
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