I noticed recently that my front passenger seatbelt is malfunctioning. While the door is closed and car is in motion, the seatbelt seems to still try to activate the same way it does when the door is initially opened/closed. Is there a sensor that needs to be replaced? I checked and the rubber stopper is still there, so I don't know what else it could be.

Looking through the system description, the only thing besides the door switch which should make it operate is the passenger's buckle switch. I imagine you'd be getting door ajar warnings if the door switch was responsible, so I think I'd try disconnecting the buckle switch and see if the misbehavior stops.