I have a 2008 Base GP, 3800 engine, about 110,000 miles, daughters car.

A couple of weeks ago she got CEL pulled the code P0420 Catalytic converter, cleared the code, car seams to be running fine, I don't drive it much.

Today she got a flashing CEL and complained about no power and a lot of vibration. Pulled the code, P0300.

I don't have my live data scanner, trying to get a hold of my buddy to get it back. What are the steps to get this diagnosed?

Thanks,
John