Lexus RX300 (MCU15). Service manual - part 337

I19259

Body ECU

Taillight Relay

G–W

B8

TRLY

To Rear 
Fog Light Relay

1J

4

7

1B

1A

1

FR FOG

1

2

5

3

To ALT
FUSE

7

Instrument Panel J/B

1B

6

1F

7

TAIL

Fog Light
Relay

(*2)

To Front Fog 
Light RH (*2)

1

2

3

5

2

1J

To Front Fog 
Light LH (*2)

To Front Fog 
Light (*1)

To Body ECU

DI–580

–

DIAGNOSTICS

BODY CONTROL SYSTEM

LEXUS RX300   (RM785E)

Taillight relay circuit

CIRCUIT DESCRIPTION

Taillight relay will be ”ON” by operating the taillight switch. The transistor which activates the tail light relay
has two sorts: one activates by the tail light switch for fail safe and the other activates by CPU.

WIRING DIAGRAM

DI1ON–19

–

DIAGNOSTICS

BODY CONTROL SYSTEM

DI–581

LEXUS RX300   (RM785E)

INSPECTION PROCEDURE

HINT:
In case of using the hand–held tester, start the inspection from step 1 and in case of not using the hand–held
tester, start from step 2.

1

Check taillight relay using hand–held tester.

PREPARATION:
Connect the hand–held tester to the DLC 3.
CHECK:
Check that the taillight relay can operate in an ACTIVE TEST.

OK

Proceed to next circuit inspection shown on
problem symptoms table (See page DI–570).

NG

2

Check taillight relay (See page BE–31).

NG

Replace the taillight relay.

OK

3

Check wireharness and connector between taillight relay and Body ECU, battery
and taillight relay.

NG

Repair or replace wireharness or connector.

OK

Proceed to next circuit inspection shown on
problem symptoms table
(See page DI–570).

I19260

Body ECU

R

B5

HRLY

12

2I

2A

To Headlight LH

(Low Beam)

1

Engine Room J/B

Head Lamp 
Relay

(*1) To High Beam Indicator Light

6

2B

1

1

MAIN

To Battery

2F

2F

2

1

2

3

4

1

2

5

2F

2F

3

H–LP RH

*1

H–LP R LWR

*2

*1: RHD Only
*2: LHD Only

(*1)

(*1)

H–LP LH

*1

H–LP L LWR

*2

To Headlight RH

(High Beam)

(*1)

To Headlight RH

(Low Beam)

To Headlight LH

(High Beam)

(*1)

(*1)

DI–582

–

DIAGNOSTICS

BODY CONTROL SYSTEM

LEXUS RX300   (RM785E)

Headlight relay circuit

CIRCUIT DESCRIPTION

Head light relay will be ”ON” by operating the headlight switch. The transistor which activates the taillight
relay has two sorts: one activates directly by the headlight switch for fail safe and the other activates by CPU.
the one that activates by CPU has two systems and prevents the headlight from turning off at the time of
one system trouble in the automatic operation circuit.

WIRING DIAGRAM

DI1OO–12

–

DIAGNOSTICS

BODY CONTROL SYSTEM

DI–583

LEXUS RX300   (RM785E)

INSPECTION PROCEDURE

HINT:
In case of using the hand–held tester, start the inspection from step 1 and in case of not using the hand–held
tester, start from step 2.

1

Check headlight relay using hand–held tester.

PREPARATION:
Connect the hand–held tester to the DLC 3.
CHECK:
Check that the headlight relay can operate in an ACTIVE TEST.
OK:
If the head light relay is normal, the head light comes ”ON”. In the case that the head light relay activates
but the head light will not come on, check the head light circuit.

OK

Proceed to next circuit inspection shown on
problem symptoms table (See page DI–570).

NG

2

Check headlight relay (See page BE–31).

NG

Replace the headlight relay.

OK

3

Check wireharness and connector between headlight relay and Body ECU, bat-
tery and headlight relay.

NG

Repair or replace wireharness or connector.

OK

Proceed to next circuit inspection shown on
problem symptoms table
(See page DI–570).