The car only has 52k miles on it. Is it really likely that the O2 has gone bad already? I've read that it could be vacuum leak somewhere or something of the sort. Would this single code leave the possibility of other problems or pretty clearly be O2?
Also, are all 4 O2 sensors the same part number? Any suggestions on the best place to order online? Upstream is the one in the manifold?
#1 on this diagram?
http://realoem.com/bmw/showparts.do?...46&hg=18&fg=10