Thank you ALL so much for the advice. I'm glad I thought about looking up something like this.

I am considering purchasing a 1999 V70 XC, it's got 168,000 miles on it. Looks pretty good. Drove it around the block, sounded great no hesitations etc, but it did have the engine light on. Seller told me he had taken it in to have it hooked up and was told it is the O2 sensor (which he said was not ...