Lexus RX300 (MCU15). Manual — part 306

I11485

E

(+)

+B2

(–)

DI–456

–

DIAGNOSTICS

THEFT DETERRENT SYSTEM

LEXUS RX300 (RM785E)

INSPECTION PROCEDURE

1

Check ECU–B fuse.

PREPARATION:
Remove ECU–B fuse from engine room junction block.
CHECK:
Check continuity 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

2

Check voltage between terminals +B2 and E of theft deterrent ECU connector.

PREPARATION:
Disconnect the theft deterrent ECU connector.
CHECK:
Measure voltage between terminals +B2 and E of theft deter-
rent ECU connector.
OK:

Voltage: 10 – 14V

OK

Proceed to next circuit inspection shown in
problem symptom table (See page DI–452).

NG

3

Check for open in harness and connector between ECU and body ground
(See page IN–32).

NG

Repair or replace harness or connector.

OK

Check and repair harness and connector be-
tween ECU and battery.

I19243

Instrument Panel J/B

Theft Deterrent ECU

11

T4

IG

Battery

5

FL Block

3

W

B–R

ECU–IG

B–Y

Ignition SW

AM1 IG1

W–L

ALT

10

ID

7

IC

AM1

1

1A

6

IC

1

2

2

4

W

–

DIAGNOSTICS

THEFT DETERRENT SYSTEM

DI–457

LEXUS RX300 (RM785E)

Ignition Switch Circuit

CIRCUIT DESCRIPTION

When the ignition switch is turned to the ACC position, battery positive voltage is applied to the terminal ACC
of the ECU. Also, if the ignition switch is turned to the ON position, battery positive voltage is applied to the
terminals ACC and IG of the ECU. When the battery positive voltage is applied to the terminal ACC of the
ECU while the theft deterrent system is activated, the warning stops. Furthermore, power supplied from the
terminals ACC and IG of the ECU is used as power for the door courtesy switch, and position switch, etc.

WIRING DIAGRAM

DI84U–01

I11484

IG

(+)

(–)

DI–458

–

DIAGNOSTICS

THEFT DETERRENT SYSTEM

LEXUS RX300 (RM785E)

INSPECTION PROCEDURE

1

Check ECU–IG fuse.

PREPARATION:
(a)

Remove the fuse box opening cover.

(b)

Remove ECU–IG fuse from instrument panel junction
block.

CHECK:
Check continuity of ECU–IG fuses.
OK:

Continuity

NG

Check for short in all the harness and compo-
nents connected to the ECU–IG fuse
(See attached wiring diagram).

OK

2

Check voltage between terminals IG of theft deterrent ECU and body ground.

PREPARATION:
(a)

Disconnect the theft deterrent ECU connectors.

(b)

Turn ignition switch ON.

CHECK:
Measure voltage between terminals IG of theft deterrent ECU
connector and body ground.
OK:

Voltage: 10 – 14V

NG

Check and repair harness and connector be-
tween theft deterrent ECU and battery
(See page IN–32).

OK

Check and replace theft deterrent ECU.

I19244

Theft Deterrent ECU

HORN Relay

T5

W–R

HORN

4

C12
Horn
S/W

H8
Horn
RH

1

6

G–W

2B

2

3

5

6

HORN

1

W

1

1

3

1

1

H7
Horn
LH

Engine Room J/B

W–R

W–R

G–W

2E

1

2I

1

W

Battery

FL Block

–

DIAGNOSTICS

THEFT DETERRENT SYSTEM

DI–459

LEXUS RX300 (RM785E)

Horn Relay Circuit

CIRCUIT DESCRIPTION

When the theft deterrent system is activated, it causes the transistor in the ECU to switch ON and OFF in
approximately 0.4 sec. cycles. This switches the horn relay ON and OFF, thus the horns blow (See the wiring
diagram below).
In this condition, if any of the following operations is done, the transistor in the ECU goes OFF and the horn
relay switches OFF, thus stopping the horns from blowing:

(1)

Unlock the doors with the wireless door lock control system.

(2)

Wait for approximately 30 seconds.

WIRING DIAGRAM

DI61A–04