I have been fighting a nagging error code for about 6 months on my 2005 C230 that has led to a replaced t/stat, O2 sensor (before cat) and now I'm told I need to just replace the cat.

No one can tell my why the cat has failed or how it failed - anyone have any ideas? Before I replace the cat (which is suposed to last for life...how long is "life") I just want to make sure that I'm not going to need another one in a few months because we aren't actually addressing the real issue.

The problem started last fall when the car had ~96K miles and began to have a very strong gasoline/amonia smell when I first turned the car on. After it warmed up the smell went away. You can only smell it outside the car. The code that came up at the same time as the smell said there was a temp error, so we changed the t/stat first, and the code went away. After driving it for ~450 miles, an O2 code came up, so we changed the O2 sensor before the cat. After driving it for another ~450 miles the code indicating a bad cat came up. Since a bad cat isn't bad for the car (or so I'm told), I've been trying other avenues to find out what is wrong. But now need to get inspected, so I absolutely have to fix the issue.

I don't mind replacing the cat, but I just want to know why it failed. Also, there are now over 100K miles on the car, and cat is out of warentee and turns out that a cat is expensive.

Any help would be greatly appreciated!

I think cat converters have an 8 year warranty since they are emissions components. Hopefully someone here knows the details, if that's true. Might be 8yr/80K mi. So you'd be SOL in that case.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra