Honda Repair: 99 Honda Civic Check Engine Light, threshold bank, cat converter

Question
Hi Tony,
I own a 1999 Civic standard shift 4 door sedan. I have recently had my mechanic (non dealership) replace my catalytic converter with a non OEM cat converter. I have had him replace both 02 sensors with Bosch sensors (upstream and downstream after the converter was replaced. I have had the the check engine light shut off and within approximately 75 miles of driving it comes back on. The codes read as follows, p0133 02 s ckt slow response 1/1. The second code is p0420 cat efficiency below threshold bank. The car is well maintained with a new timing belt and 166000 miles. I drive it to work approximately 50+ miles one way per day. I would really like to get this problem solved. I know alldata has some tsb's on this, is there a flash available to update the computer? Is this converter being non oem the problem? I have had everything replaced including the purge control valve (which resolved that code) which the computer said was bad.  I am at wits end.  The car gets between 36-40 mpg and runs real well.   thank you for your time,
Craig

Answer
Ok. Sorry its taken me a minute to respond. As for the p0133, your going to probably need to get an updated pcm. No flash update is provided for this, only the updated pcm. The p0420 reappearing is a common problem with after market cats, although Ive seen it more on odysseys. I think the after market ones are just not as good quality or don't use the same precious metals as the factory ones.