Automatic control and headlight range adjustment (Discovery 3)

Automatic headlight control

The automatic headlight function serves to assist the driver. The driver can override it by turning on the parking lights or headlights if the ambient light level is low and it is necessary to turn on the front or rear lights. The automatic headlight control system uses a light sensor and a CJB unit connected to the sensor by a local LIN data bus.
The light sensor is included in the rain / light sensor located on the inside of the windshield, under the rearview mirror. The wiper system also uses a rain/light sensor to automatically control the wipers. For more information contact Wipers and Washers (501-16 Wipers and Washers)

The sunlight sensor measures the level of illumination of the vehicle, both in the vertical direction and the lateral illumination of its front. During operation, the rain / light sensor uses information about the speed of the vehicle, the position of the wiper switch, as well as the position «parking» wiper blades.

The automatic headlight control uses an ambient light signal that is measured by a photodiode built into the rain sensor. The rain / light sensor, via the local LIN bus, sends a request to the CJB to turn the lighting on or off, which responds to the request by turning on the dipped beam headlights, front and rear position lights.

The automatic headlight control system is activated under the following conditions:

• Twilight
• Night time
• Rain
• Snow
• Tunnels
• Underground or multi-storey car parks

For the automatic headlight control system to work, the ignition key must be in position II, the light switch in position «AUTO», and the sunlight sensor should signal the activation of the system.

Headlight range adjustment

Headlight range adjustment is designed to adjust the vertical axis of the headlights. The main purpose of the system is to prevent blinding of drivers of oncoming vehicles and other road users when the rear of the car is heavily loaded.


Vehicles are equipped with one of three headlight range adjustment systems: manual, static and dynamic.

Manual headlight range adjustment

The manual headlight range adjustment is only fitted to vehicles with halogen headlights and coil-spring suspension.

The dynamic headlight range adjustment includes the following components:

• Two electric motors for headlight range adjustment
• Rotary switch for headlight beam adjustment rheostat

In ignition key position II, power is supplied to the light switch through the ignition relay, which is located in the battery junction box (BJB), and on to the tilt motor for each headlight assembly via the CJB. When the light switch is turned to position lamps on or headlights on, power is supplied from the ignition relay to the headlight range control rotary switch.

Turning the headlight beam adjustment switch generates different voltages that are sensed by the electric motors. The electric motors respond to the applied voltage and move the headlights to a predetermined position, which corresponds to the amount of voltage applied from the rotary switch.

The headlights can be lowered from the unladen position to compensate for changes in vehicle rear suspension height caused by axle load.

Static headlight range adjustment

Static headlight range adjustment is only available on vehicles with air suspension.

Static headlight range adjustment is performed by the vehicle's air suspension and air suspension controller. The suspension control system continuously monitors the vehicle's position and automatically adjusts the height of the front and/or rear suspension. In this case, the position of the body remains almost horizontal and, therefore, the correct direction of the headlight beams is constantly maintained.


The body stabilization system operates fully automatically, so there is no manual headlight range control on the light switch.

Dynamic headlight range adjustment (for models with air suspension)

Dynamic headlight range adjustment is only available on vehicles with AFS and air suspension.

The dynamic headlight beam throw adjustment system automatically adjusts the headlights vertically at high speed, which allows you to adjust the headlights during sudden acceleration and braking of the car.

The dynamic headlight range control operates fully automatically, so there is no manual headlight range control on the light switch.

NOTE: The AFS system works in conjunction with the body stabilization system as described above.

The dynamic headlight range adjustment includes the following components:

• Two electric motors for headlight range adjustment
• AFS controller
• Engine confirmation signal from the engine control unit
• Vehicle speed signal from ABS controller
• Body Height Information from Air Suspension Controller

In ignition key position II, power is supplied to the light switch via the ignition relay, which is located in the battery junction box (BJB), and further to the AFS controller. When the light switch is turned to position lights on or headlights on, power is supplied from the ignition system relay to the AFS controller.

NOTE: When signaled to turn on the ignition, the AFS controller initiates both the AFS system and the headlight range adjustment motors. Details of the initiation procedure are set out above in the description of the AFS system.

The system is controlled by the AFS controller, which receives via the CAN bus information about the height of the front and rear suspension from the air suspension controller, information about engine operation from the engine control unit, as well as information about the speed and brake pedal pressure (on the inclusion of brake lights) from the ABS controller. The AFS controller processes the received information and sends control signals to the headlight range adjustment motors to adjust the vertical position of the headlights in accordance with the position of the body and the speed of the vehicle.

NOTE: For markets where vehicles are supplied with daytime running lights (DRL), the dynamic headlight beam throw adjustment does not work when the DRL system is on.