[Frenchies_M5]

Hey guys my '13 m5 just threw the engine light. Stopped by an auto advance to borrow their machine to read the codes since the car wasn't saying anything other than the light. It came up with the error p0420 which is catalyst system efficiency below threshold bank. Any body know what that could be. I recently got a muffler delete done on the car. (aprox. 2weeks ago).