When I bought my car it had a ridiculous frankenstein of an exhaust on it that droned like crazy and had multiple exhaust leaks. I have since removed the crappy jiffylube special cats and exhaust and put on a Corsa with a piece of pipe where the cat used to be. The car didn't seem to notice or care for a few hundred miles, then randomly threw a check engine light. I checked the code and it was an 02 sensor failure code. Why did the car wait so long to throw a code? If that happens again will the car go into limp mode and/or run super rich, or will it just be an engine light reminding me to fix the cats? I can deal with a CEL being on for a little while, but obviously will have to get new cats asap if this is going to impact my performance.