almost 70,000 miles on it. I haven't picked the car back up yet. I agreed to some other work I needed done, so I'll ask him to elaborate more on how he determined that 2 needed replaced.

He told me both "front O2 sensors". I presume that to mean both "pre-cat" (though I'll double check this too), which if I understand right would be both on my left as I'm looking down at the engine. The one closest to the front I can see. I can't easily see the one further back towards the firewall, which makes me ask how much effort is involved moving things to get to it if I should do this myself?