Odd DME behavior-emission issues

[jontalk]

I've had my 01 Boxster S for about 5 years now and it recently turned 80K miles. About a year after I bought it the CEL came on and threw code P0420 several times, so the shop recommended I drive the car harder whicht seemed to clear the problem. Then it threw the same code and we replaced both pre-cat O2 sensors at 70 K miles.

About 6 mos. later the same code showed up again. We cleared the code and months later the CEL came on again and said the Bank 2 Cat was aging. I put some fuel additive in it which seemed to have helped. When I went to smog the car for CA registration about 18 mos ago, it wouldn't pass. I had the MAF and air filter cleaned; it turned out the alternator was on the way out and wasn't charging properly which is why it wouldn't pass smog. Once that was corrected it passed smog with nearly new car emission stats!


A year or so later it threw the P0420 code again and it was decided to swap the O2 sensors around. The car has an oil service with fuel additive at that point as well and several months went by without a problem.


And then once again the aging O2 sensor code showed up but on Bank 2. We replaced it with a previously used one which seemed to help until a week or so ago when it threw the same code. The shop decided to reinstall and update the DME software and a few days later the CEL came on again. Today when I went to the shop it showed code P0830 which states BOTH cats are bad. DOH!!

In all my years driving I've never had a car with such a weird problem. The car runs great, handles like a gem but this is crazy! I'm NOT replacing the CATS on this car that's for sure! Any ideas gang?