So I was on a trip last week out of town and my battery died. Just as a heavy huge rain storm was approaching. Called AAA they guy put in a new battery, but had an unusually hard time with it - seemed like he didn't know what he was doing. Anyway, during the 30 mins it took this guy to figure out taking out the bad battery and putting in the new one, rain poured into the open hood and all over everything in the engine compartment. On top of that, the guy insisted on testing both batteries by struggling to find some piece of metal to clamp on the negative connection to, rather than using the black battery post. While he was doing this, he seemed to try and fail searching for some piece of metal to clamp the thing on, and I saw this thing slip off repeatedly from whatever he had tried last. Anyway, fast forward to a few days ago - I get a CEL which is unusual for the middle of summer. I have a recurring p0440 or p0442 but that happens in the winter, so I figured I better get the codes read. It comes back a p0130 bad o2 sensor. Now this is a code I haven't had before and I wouldn't be shocked just based on mileage or age if one or both of them needed to be replaced, but is sure is a huge coincidence that this guy was screwing around under there in the rain last week and then this code appears. I am thinking he broke one of the connector or wires or that some of that rain got in to the sensor and is messing it up. I haven't had a chance to closely inspect things yet.

So my questions are - is there a way to know which (upstream of downstream) the potentially bad sensor is based on the p0130 code? How big a deal is it to just ignore it and keep driving around if I am not having any other performance or gas mileage issues? Is it possible to squeeze under the car and change the downstream sensor without raising the vehicle?

Any other info or suggestions related - would be appreciated.

Thx