I have recently purchased an Audi. It has 54k miles on it and engine light came on today. Readings showed code p200200. What could be causing this and how much would the repair be? 

If bought from a dealer you can return it for a full refund or free repair in the first 30 days after sale. 

It was bought from the dealer. Quiet far away as 2 hour drive. I did do a part exchange so idk how this would work. 
I do love the car already just wonder what could be wrong with it really.

DPF and or EGR Cooler. It can get expensive depending on individual circumstances. I would contact the garage, irrespective if it’s 2 hours away. The part-exchange shouldn’t affect anything.

I contacted the garage and they are suppose to get in touch with me.

this is stressful. 
 

It drives fine, the engine light disappeared and has not been on atm but I don’t want it to get proper bad.