My wife has a '98 V70 AWD. We've got just over 60K on the clock right now. The check engine light has come on twice in the past month. The first time, our shop checked the codes which told him that the gas cap had been loose. He cleared the codes, we tightened the gas cap and had happy motoring for a few weeks. My wife then fills up and leaves the gas cap off, driving away from the station. Yep, the check engine light comes back on. She gets a replacement cap, puts it on and asks the dealer if they could check and clear the codes for her. They didn't have time and told her that the check engine light should clear itself by 100 miles if the condition that prompted the light to come on was no longer happening. This is the first I've heard of this and wanted to know from everyone if that was possible? We've driven close to 300 miles since the light came on. The assumption is that it is on for the gas cap issue again, but naturally we don't know the answer for that unless we have it checked. Can the check engine light extinguish itself?