BMw 328 i 1997 Check engine light came on the next day after an oil change/fuel filter change and a half tank fill up. Took it to BMW according to their Diagnosis I have the papers its code 234? It says no fault currently present. Then it says Cat converter effieciency to low then on other paper it says too large in rich range. Then it says oxygen sensor heater 1 55%. I was going to my first dealer who put in a new cat conv at no charge(under warranty) at 69,000. It seems strange that at 130,000 I would need a new converter and 2 sensors for 2,000 dollars!!! Well the day before my appointment it went off. Seemed odd that an additional 60,000 on a new cat converter needs replacing. Anyhow car runs fine got a new gas cap anyhow and we'll see.(have not put it on yet) It amazes me how BMw told me I need all of this new stuff, when I do not believe its so. Trick is find an honest nice guy who has a brain in his head or do all you can yourself?