Lexus LS400 (2000 year). Service manual — part 59

I03250

Connect the wire harness side connector to the
rheostat light control, and check the connector
on the wire harness side from behind.

Put a cover over the automatic light control
sensor so that light does not reach it.
Turn ignition switch to ON and light control
switch to TAIL.

Connect the (+) lead from voltmeter to

terminal 5, and the (–) lead to the body ground.
Is there battery positive voltage?

Connect the (+) lead from the voltmeter

to terminal 6, and the (–) lead to the body

ground. Is there battery positive voltage?

Is there continuity when the ohmmeter is

connected to terminal 7 and the body ground?

Is there continuity when the ohmmeter is

connected to terminal 9 and the body ground?

No

Replace rheostat light control.
Then recheck system.

Yes

Put the voltmeter ins AC mode (alternating current
made).
Connect the voltmeter (+) lead to terminal 3 and
the (–) lead to connector terminal 17.
Does the voltmeter readout change as the rheostat
light control is turned clockwise and
counterclockwise?
(The rheostat light control registers approx. 0 V
when turned fully clockwise.)

No

Replace rheostat light control.
Then recheck system.

Yes

Connect a 3.4 W test bulb between connector
terminals 8 and 7. Does the bulb brightness
change when the rheostat light control is
turned clockwise and counterclockwise?

No

Replace rheostat light control.
Then recheck system.

Remove only connector terminal 2 from the
vehicle harness.
Connect the voltmeter (+) lead to terminal 2 and
the voltmeter (–) lead to terminal 9.
With the rheostat light control turned fully
clockwise, turn it further clockwise beyond the
moderate.
Does the voltage change from 0 V to battery
voltage?

Yes

No

Replace rheostat light control.
Then recheck system.

Repair or replace wire harness.

Yes

BE–64

–

BODY ELECTRICAL

ILLUMINATION LIGHT SYSTEM

1927

I03251

2

Only the combination meter cannot be adjusted

HINT: While carrying out the following inspection, make certain that the connectors and terminals are properly

connected.

Check the combination meter illumination.
Meter illumination is normal?

No

Repair or replace combination meter.
Then recheck system.

Yes

Connect the wire harness side connector to the
rheostat light control and inspect wire harness
side connector from the back side, as shown.

Yes

Put a cover over the automatic light control so

that light does not reach it.
Put the voltmeter in AC mode (alternating current mode).
Connect the voltmeter (+) lead to terminal 3,
and the (–) lead to terminal 7.
Does the voltmeter reading change as the rheostat
light control is turned clockwise and counterclockwise?

(The rheostat light control registers approx. 0 V

when turned fully clockwise.)

Replace rheostat light control.
Then recheck system.

Yes

No

Replace wire harness between combination
meter and rheostat light control.

3

The combination meter can be adjusted, but not other illumination

HINT: While carrying out the following inspection, make certain that the connectors and terminals are properly

connected.

Connect the wire harness side connector to the
rheostat light control and inspect wire harness
side connector from the back side, as shown.

Replace rheostat light control.
Then recheck system.

Put a cover over the automatic light control so that
light does not reach it.

Connect a 3.4 W test bulb between connector
terminals 8 and 7. Does the bulb brightness
change when the rheostat light control is turned
clockwise and counterclockwise?

Yes

Repair or replace the circuit of each system or wire
harness.

No

–

BODY ELECTRICAL

ILLUMINATION LIGHT SYSTEM

BE–65

1928

I03252

4

Tail cancellation does not work for the clock, air conditioner panel or combination meter

HINT: While carrying out the following inspection, make certain that the connectors and terminals are properly
connected.

Connect the wire harness side connector to the
rheostat light control and inspect wire harness
side connector from the back side, as shown.

Put a cover over the automatic light control sensor so
that light does not reach it.
Turn ignition switch to ON and light control switch to TAIL.
Remove only connector terminal 2 from the vehicle
harness.
Connect the voltmeter (+) lead to terminal 2, and
voltmeter (–) lead to terminal 9.
With the rheostat right control turned fully clockwise,
turn it further clockwise beyond the moderate.
Does the voltage change from 0 V to battery positive
voltage?

No

Yes

Replace rheostat light control.
Then recheck system.

Repair or replace wire harness.

5

Tail cancellation does not work for one of clock, air conditioner panel or combination meter.

HINT: While carrying out the following inspection, make certain that the connectors and terminals are properly
connected.

Clock

Check the clock illumination.
Clock illumination is normal?

No

Yes

Replace clock.

Replace wire harness between the rheostat and
the clock

Air conditioner panel

Check the air conditioner panel illumination.
Air conditioner panel illumination is normal?

No

Yes

Replace air conditioner panel.

Replace wire harness between rheostat light control
and air conditioner panel.

Combination meter

Check the combination meter illumination.
Combination meter illumination is normal?

No

Yes

Replace combination meter.

Replace wire harness between rheostat light control
and combination meter.

BE–66

–

BODY ELECTRICAL

ILLUMINATION LIGHT SYSTEM

1929

I03253

6

Tail cancellation (illumination at 100% brightness) does not occur when tail cancellation of the
rheostat light control is released, the light control switch is put on AUTO and light strikes the auto-
matic light control sensor.
(Area surrounding vehicle is dark.)

Automatic light control system is normal?
(See page

BE–38

)

HINT: While carrying out the following inspection, make certain that the connectors and terminals are properly
connected.

No

Replace automatic light control sensor.
Then recheck system.

Disconnect connector between rheostat light
control and automatic light control sensor, and
inspect connector on wire harness side.

Yes

Is there continuity when an ohmmeter is
connected between terminal 1 of rheostat side
connector and terminal 8 of sensor side connector.

No

Replace wire harness between terminal 1 of
rheostat side connector and terminal 8 of sensor
side connector. Then recheck system.

Is there continuity when an ohmmeter is
connected between terminal 10 of rheostat side
connector and terminal 4 of sensor side connector.

Yes

Replace wire harness between terminal 10 of
rheostat side connector and terminal 4 of sensor
side connector. Then recheck system.

Replace rheostat light control.
Then recheck system.

Yes

No

–

BODY ELECTRICAL

ILLUMINATION LIGHT SYSTEM

BE–67

1930