Had a similar problem. CEL came on in my VW. Now, there is no VW dealer for 200 miles. (I know, I know, what kind of idiot buys a brand of car that can't be serviced ANYwhere in the state in which he/she lives? Answer: me, apparently.)

So, I take it down to AutoZone as the only resort. They tell me I need a new O2 sensor, $400 dollars. Yikes.

So, I start messing with it a bit first. I decide to change the air filter, reset the OBD, and cross my fingers. I open up the air filter cover, and literally 2 cups of sunflower seeds fall out. Ummmm ... that might be an issue.

Mice were collecting them out of the birdseed I spread for the birdies and storing them in my Beetle's air filter! Poor Ringo! So, even though I felt bad, I stopped feeding the birds, and the mice moved on.