http://www.danielsternlighting.com/tech/aim/aim.html
Causes of misaligned headlights:
- Aftermarket Headlights
- Modified Headlights
- Broken Headlight Mounting Brackets or Adjusters (check after an accident)
- You've been in an Accident
- You've changed your Tires (different size, winter tires/summer tires)
- Change of Tire Pressure (due to load or temperature)
- Load in your Car (especially in the back)
- Change of a Lightbulb
- Hitting a Large Pothole