Lexus ES300 (2002 year). Service manual - part 80

BODY ELECTRICAL – ACCESSORIES

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Dark

Bright

Rear Light

Fig. 2

Reflection
Rate

AUTO Mode

During daytime driving, the inside and outside
rear view mirrors remain in the DAY mode.
The automatic glare-resistant circuit detects the
surrounding light through its No. 1 sensor, the
rear light through its No. 2 sensor, and deter-
mines whether it is day or night through the in-
tensity of the surrounding light. At the same
time, the intensity of the glare from the rear is de-
termined through the difference in intensity be-
tween the surrounding and rear light.
When the automatic glare-resistant circuit deter-
mines that the rear light is too bright, the EC
drive circuit applies voltage to the inside and out-
side rear view mirror cells to vary their reflection
rate.
In accordance with the intensity of the rear light,
the inside and outside rear view mirror’s reflec-
tion rate varies steplessly (Fig. 2).

BODY ELECTRICAL – LIGHTING

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Actuator

Headlight 
Beam Level 
Control ECU

Skid Control
ECU

Occupant 
Detection 
Sensor

Seat Belt 
Buckle 
Switch

Rear Height 
Control Sensor 
(RH only)

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Actuators

Headlight 
Beam Level 
Control ECU

Skid Control 
ECU

Rear Height 
Control Sensor

AUTOMATIC HEADLIGHT BEAM LEVEL CONTROL SYSTEM

1. General

 The automatic headlight beam level control system regulates the orientation of the reflectors of the head-

lights in relation to the posture of the vehicle that has been detected by sensors. Thus, it is a system that
maintains the headlight beams to a constant level while the vehicle is being driven.

 On the ’01 ES300, the headlight beam level control ECU assessed the vehicle’s posture through the signals

from the rear height control sensor. On the ’02 ES300, however, another piece of information has been
added to the information that is used for assessing the vehicle’s posture. The additional information deter-
mines whether or not the front passenger seat is occupied. This is accomplished by way of the ON / OFF
signal of the occupant detection sensor, which is built into the front passenger seat, and the seat belt buckle
switch. As a result, the precision of this system has been improved.

 System Diagram 



2. Layout of Main Component

BODY ELECTRICAL – LIGHTING

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Rear Height Control Sensor

Control Link

Service Tip

The headlight beam level control ECU has the initial value of the rear height control sensor stored in
its memory. Therefore, if a repair that alters the output value of the rear height control sensor has been
performed (such as the removal and reinstallation of the rear height control sensor or the suspension),
it is necessary to initialize the sensor and adjust the beams. For details, refer to the 2002 LEXUS ES300
Repair Manual (Pub. No. RM911U).

3. Construction

Headlight Beam Level control ECU

Based on the signals that are transmitted by height control sensors, the occupant detection sensor and the
skid control ECU, this ECU detects the amount of variance of the vehicle posture.
Based on the detected value, this ECU outputs control signal to the actuator.
The headlight beam level control ECU provides initial set control and fail-safe function.

Rear Height Control Sensor

The rear height control sensor detects the amount of variance of the vehicle height while the vehicle is being
driven, and output this amount in the form of signal to the headlight beam level control ECU.
This sensor is located in the rear right suspension.

Occupant Detection Sensor and Seat Belt Buckle Switch

The ON/ OFF signals of the occupant detection sensor that is built into the front passenger seat and the seat
belt buckle switch determine whether the front passenger seat is occupied. The signals are then transmitted
to the headlight beam level control ECU. The occupant detection sensor is shared with the seat belt warning
system.

Skid control ECU

The skid control ECU outputs the wheel speeds to the headlight beam level control ECU. The wheel speeds
are calculated based on the signals which are received from the speed sensors which are part of the ABS.

Actuator

Based on the signals received from the headlight beam level control ECU, each actuator moves the reflector
in the headlight to vary its beam. This actuator uses a step motor to precisely regulate the angle of the reflec-
tor.

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4. Operation

While the vehicle is being driven, the rear height control sensor detects the vehicle’s posture that varies in
accordance with the road conditions or driving conditions. The resultant signals are then output to the head-
light beam level control ECU. Based on these signals from the sensor, the ECU assesses the vehicle’s posture.
If the front passenger seat is occupied, as determined by the ON / OFF signals from the occupant detection
sensor that is built into the front passenger seat and the seat belt buckle switch, control is effected by making
a correction to the vehicle posture information provided by the rear height control sensor.
In addition, the Skid Control ECU sends the vehicle speed signal to the headlight beam level control ECU,
allowing the this ECU to determine the vehicle’s driving conditions.
This ECU controls the actuator so as to cancel out the changes in the light beams that are caused by these
changes in the vehicle’s posture and speed.

5. Fail-Safe Function

The headlight beam level control ECU operates in
the fail-safe mode if an abnormal condition such
as those listed below has been detected, and ?illu-
minates the automatic headlight leveling system
warning light in the combination meter.

Item

Abnormality Detection Condition

Description of Control

Actuator

Open or Short

Holds the beam at the position of the actuator
when the abnormality has been detected.

Rear

Returns the beam to the actuator’s initial set
position if an abnormality has been detected
higher than the initial set position.

Rear
Height Control
Sensor

Signal Level Abnormality

Holds the beam at the position of the actuator
when an abnormality has been detected, if the
abnormality has been detected lower than the
initial set position.

Headlight
Beam Level
Control ECU

When an abnormal processing of the
CPU has been detected.

Holds the beam at position of the actuator when
the abnormality has been detected.