If you go by a Volvo service deparment (or certified volvo repair shop) and ask nicely, they will usually reset it for you for no charge. This has happened to me a couple of times and they finally told me that volvo certified mechanics are supposed to reset the light for you when they change your oil. Since I bought the car used, I didn't know this and had just been going to the local jiffy lube, which apparently had no idea about all of this. An incentive to take your car to the Volvo dealer for an oil change, I guess.