I have 3 friends all with different color and year Impalas.. All have had various light issues. Low beams not working seems to be the only one they all have in common. Other issues are fill with water and bulb breaks.. another is High beams only stay on if you hold the lever (doesn't make clicking). Another was daylight headlamps not working. In my opinion all these issues have to be caused by one thing either a defective assembly or sensor.. eventually one of these owners tracked a previous owner who informed him this was a major reason for getting rid of the car and buying a new one..