I posted on this before due to the problem I was having with all 5 of the same sensors. First the MAF, and then one by one all 4 of the O2 sensors would give codes. I would have replaced them all at once but my extended warranty covered everything and as such I had to wait as each one caused a code. This happened about every other week until all were replaced. MN had a great link a while back about O2 sensors and the moral of the story is that these do degrade over time and when one goes or has a few miles on them you should replace ALL OF THEM at once. It costs a bit, but man it does make a difference. New life!!!
