Automatic control and headlight leveling (Discovery 3)

Automatic headlight control

The automatic headlight function is a driver assistance function. The driver can override it by turning on the side lights or headlights when the ambient light level is low and the front or rear lights need to be turned on. The automatic headlight control system uses a light sensor and a CJB unit linked to the sensor via a local LIN data bus.
The light sensor is integrated into the rain/light sensor, located on the inside of the windshield, below the rearview mirror. The windshield wiper system also uses the rain/light sensor to automatically control the windshield wipers. For more information, contact Wipers and Washers (501-16 Wipers and Washers)

The sun sensor measures the level of illumination of the vehicle, both vertically and lateral illumination of its front part. During operation, the rain/light sensor uses information about the vehicle speed, the position of the windshield wiper switch, and the "parking" position of the windshield wipers.

The automatic headlamp control mode uses a signal from the ambient light, which is measured by a photodiode integrated into the rain sensor. The rain/light sensor, via the local LIN bus, sends a request to the CJB to turn the lights on or off, which responds to the request by turning on the low beam headlamps, front and rear side lamps.



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

• Twilight
• Dark time of day
• Rain
• Snow
• Tunnels
• Underground or multi-storey car parks

For the automatic headlight control system to operate, the ignition key must be in position II, the light switch must be in the "AUTO" position, and the sunlight sensor must provide a signal to activate the system.

Headlight leveling correction

The headlight tilt adjustment is designed to adjust the vertical axis of the headlights. The main purpose of the system is to prevent blinding oncoming drivers and other road users when the rear of the vehicle is heavily loaded.

Cars are equipped with one of three headlight leveling systems: manual, static and dynamic.

Manual headlight leveling

The manual headlight leveling system is only installed on vehicles with halogen headlights and coil spring suspension.

The dynamic headlight leveling system includes the following components:

• Two electric motors for headlight leveling
• Rotary switch for controlling the headlight leveling system rheostat

When the ignition key is in position II, power is supplied to the light switch via the ignition relay, which is located in the battery junction box (BJB), and then to the headlamp leveling motor of each headlamp unit via the CJB. When the light switch is turned to the parking lamp or headlamp position, power is supplied from the ignition relay to the rotary switch for the headlamp leveling system.

When the headlight leveling switch is turned, different voltages are generated and sensed by the electric motors. The electric motors respond to the applied voltage and move the headlights to a predetermined position that corresponds to the voltage applied by the rotary switch.



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

Static headlight leveling

The static headlight leveling system is only installed on vehicles with air suspension.

Static headlight leveling 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. At the same time, the body position remains virtually horizontal and, therefore, the correct direction of the headlight beams is constantly maintained.

The body stabilization system operates completely automatically, so there is no manual headlight leveling adjustment on the light switch.

Dynamic headlight leveling (for models with air suspension)

The dynamic headlight leveling system is only installed on vehicles with the AFS system and air suspension.

The dynamic headlight leveling system automatically adjusts the vertical position of the headlights at high speed, allowing the headlights to be adjusted during sudden acceleration and braking of the vehicle.

The dynamic headlight leveling system operates completely automatically, so there is no manual headlight leveling adjustment on the light switch.

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

The dynamic headlight leveling system includes the following components:

• Two electric motors for headlight leveling
• AFS Controller
• Engine operation confirmation signal from the engine control unit
• Vehicle speed signal from ABS controller
• Ride height information from air suspension controller

When the ignition key is in position II, power is supplied to the light switch via the ignition relay, which is located in the battery junction box (BJB), and then to the AFS controller. When the light switch is turned to the parking light or headlight position, power is supplied from the ignition relay to the AFS controller.

NOTE: When the ignition switch is turned on, the AFS controller initiates both the AFS system and the headlamp leveling motors. Details of the initiation procedure are provided above in the AFS description.

The system is controlled by the AFS controller, which receives information on the height of the front and rear suspension from the air suspension controller, information on engine operation from the engine control unit, as well as information on the speed of movement and pressing of the brake pedal via the CAN bus. (about turning on the brake lights) from the ABS controller. The AFS controller processes the received information and sends control signals to the headlight leveling 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 the Daytime Running Light (DRL) system, the Dynamic Headlamp Leveling system does not operate when the DRL system is on.