So I just recently bought a 2015 Audi A4 with a 2.0T b8.5 engine through a private party. I paid $8500, has 149k on dash. I intended to just buy this car to flip it & make a little cash. Anyways, the guy who sold it to me said nothing was wrong with it. Within 30 minutes after purchasing the check engine light came on. Obviously he must of reset the code. The car runs beautifully, car was also kept in mint condition cosmetically inside & out. I’ve considered even keeping it because of how clean it drives and looks. I used half of my savings to get this car & I don’t want to be a douche like this guy and sell it to someone else and reset the code and play dumb, (since visually the car sells it self as well as how smooth it drives). What is the best way about going about this? I will say since buying the car my oil level when checking on the system was halfway when I bought it, after one day of driving it less then 100 miles it has dropped to a quarter on the bar level. I know these engine tend to lose oil a lot but this is very excessive. Now with the code coming up as a catalytic converter and the engine losing excessive oil what should I do, I’m not rich & definitely can’t afford to lose out on the $8500 I spent, I’m willing to fix it if the repair isn’t nothing over 2-3k , but I want to be sure it will fix the problem. Please help, want to get an idea before bringing it to Audi. 
FYI: I can’t tell if the engine is leaking since the bottom of the car has one of those plastic covers but like I said car runs great! I will say, at times I’ve smelled almost like burnt oil , can’t really tell if it’s from the AC unit or coming from the engine. I’m no mechanic & know the basics when it comes to cars . Other then that, cars drives beautifully, please help.