Air Bag Light On problems of the 2006 Volvo S40

2006 Volvo S40 passenger side air bag sensor is malfunctioning. When a passenger is sitting in the passenger seat, the airbag light saying that the airbag is off is often illuminated, but not always. The dealer has told me that they have encountered this problem on several 2006, 2007, and 2008 models. They initially told me that this was normal behavior. They are now investigating since I have raised the safety concern of being in the passenger seat and not having the airbag deploy. This is the third time we have had our car in for this problem. The dealer is working with Volvo to fix this problem, but it seems like there may be a number of defective sensors out there.