Hi,
I have a 99 S-80 T6. WE are around 78,000 miles. Several months ago the car started the Emission System Service Required. That would stay on for 3 days then off 3 days. On day 2 the check engine light would come on & stay on 2 days, then 3 days no messages. I asked this site & someone said try STP. That it was probably the throttle. I also had no difference in performance. I tried the STP two times in a row. The rate of the message changed. It was no longer regular, after a month of regularlarity. We bought a Infiniti G-35 & parked the volvo. I drive it once a week. Since I am driving it less the message has not yet reappeared. I can't sell the volvo while in Canada. When we return to the US we plan to donate it to a charity. I could not in good conscience sell it to anyone else. It breaks down regularly. Best of Luck, Sandy