General Information

General Information

Automatic headlight adjustment is required on vehicles with High Intensity Gas Discharge (HID) headlights.

Automatic vertical headlight aim control system keeps the low beams at a constant level even if the car is loaded, a situation which would normally change the headlight angle.

There are two vehicle level sensors, one on the front axle and one on the rear axle. These sensors register the vehicle's fore/aft angle of inclination. The Vehicle Speed Signal (VSS) is also processed.

The control module evaluates these signals and activates the headlight beam adjusting motors when low beams are on.

Function
The automatic vertical headlight aim control system consists of:
- Automatic vertical headlight aim control system control module -J431-
- Left rear level control system sensor -G76-
- Left front level control system sensor -G78-
- Right headlight beam adjusting motor -V48-
- Left headlight beam adjusting motor -V49-

When starting the engine, vehicle level is measured and compared to the set point. This signal is sent to the headlight beam adjusting motors which adjust headlight position to this value once, whether or not the low beams are on.

After this single correction, signals to change low beam position will only be sent to the headlight beam adjusting motors with the low beams on.

If a trip is interrupted (vehicle speed less than 1 km/h) and a vehicle position change is recognized due to additional weight (e.g. extra people in the car) the headlights will be automatically adjusted to the proper height.

All changes made by the automatic vertical headlight aim control system are due to static operating conditions.

NOTE: The following description is only relevant for the VAG1551 scan tool.