I have a 1998 Olds Achieva that has 123,000 miles. For the last several months I have had problems with the check engine light not going off. An 02 sensor was replaced and a week later the light came back on. I took it to a new shop and they put a catalytic converter on and the light stayed off for a while then came back on. At no charge they put another cat converter on and it has been fine for about three months now, but a few days ago it came back on. GRRRR~~ Now I also have an additional new problem. The ets light and the abs light will come on at the same time. Cut engine off and restart and the lights go off. This doesn't happen all the time but it does happen every few days. Also, the low trac light will come on for about a minute or two and then go off. Any ideas??