What does code 0DEE mean on a 2002 Chevy Blazer?

It is a code that means you need to replace your Catalytic converter(s) but it could be brought on by other components in your emissions system that need to be replaced as well. Check your Converter(s) by knocking on them. If they sound solid, (not hollow), then they probably need to be replaced. If they sound hollow, then replace the PCV valve first to determine if you have a bad one. It is the cheapest fix that is usually the solution. Check your engine's performance after you change any component on it. If that doesn't solve the problem check for a vacumme leak in the emissions system by checking hoses. Make sure to replace any hoses that are faulty and to secure them off of the engine, either by their brackets or with zip ties. Lastly, if your problem isn't solved, then replace the O2 sensor and then the EGR valve respectively checking to see if that solves your problem. Lastly if all these components have been changed and if you are still experiencing the issue then you probably still need to change the converter(s). After you find and solve this problem, you will need to either take your vehicle to the dealer to have the codes reset, or reset them yourself. There are tutorials online for that. I hope this helps because that is how I solved the problem with my 2002 Blazer.