I have a 1998 S70 and assume our circumstances are the same. My service light came on and was reset by the dealer during a maintenance visit. However, I checked about reseting the light with www.AllDataDIY.com, a web-based site with on-line maintenance information (for a fee). Though their information was initially incorrect, they sent me updated stuff that may work for you. They say (per a copyrighted Volvo bulletin) that the Service Indicator can be reset with the following procedure (parenthetical fragments are my guesses as to what Volvo meant):

1. (Start with) ignition off
2. Press in the trip odometer reset button (and hold)
3. Switch on ignition
4. Continue pressing in the reset button for 10 seconds
5. Release the reset button within 4 seconds (after light goes off)

If you still have your light on, try this with some variations to see if it works. I would appreciate a response about your success or failure, since I cannot test this procedure for quite a while.

Gene

ggrunby@yahoo.com