My check engine light came on when the car had less than 80K on it. I brought it to the dealer and they replaced the #2 oxygen sensor, bank 1. The check engine light came on shortly afterward. So I brought it back to the dealer. They told me it must be the Catalytic converter. I did not have it replaced because I thought they were wrong. I did not smell anything or see any smoke.
Later on the car would not pass Massachusetts inspection because the check engine light was on. According to the scanner the error code P0420 kept coming up. At 1 point an error P0136 so I again replaced #2 O2 censor and kept reading P0420. I then installed a straight cell fix and the check engine light did not come back on and the car passed inspection. The straight cell fix can be also hfound at O2 Simulator, mini catalytic Converter cel fix they also have a mini cat at that site but I didn't put out for the extra bucks, and besides, the straight cell worked great.