[koffinb]

I have a 2006 330i with a little over 200k miles on it. Car runs great, but a few weeks ago I had my CEL come on and scanned it with a generic OBD scanner. Came back as 'P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)'. I have also been getting really bad MPGs lately as well.

Any idea on what could be going on? I was thinking may O2 sensor? Anyone else have a similar experience with this code?