Recently my 96GT started giving me codes p0420 and p0430. They are "catalyst system efficiency below threshold" codes. Here is the thing. I did have a Hypertech powerchip on my computer but had to take it off because I put a 180 thermostat on the car which for some reason was causing the fan to run constantly. Shortly after I took the powerchip out I started to get these codes. I actually have a BBK catted h-pipe on it so I am still emissions legal. Do you think there is any connection with the now "stock" computer having a problem with my catted pipe? This is frustrating because of still being emissions legal but now Im getting these codes. Any help would be appreciated.