Hello! First post on here so feel free to correct me if I'm in the wrong spot or not giving enough info. Any advice or rant is appreciated as I'm starting to get desperate. Thanks in advance.

I'm looking just for info and not so much to do DIY repairs, but I have a real pickle. I bought this Honda Fit 2011 about 3 years ago used. Another owner had it for the first 6 years. About 6 months ago the engine blew up. No idea what happened or what caused it. There was a loud bang and spark plug launched into the engine apparently. I had it towed to a repair place and they put in an entirely new engine. This was pretty costly for me at the time so I got the car mostly fixed. There was just an issue with the O2 sensor. One that is a dual sensor and cost about $300. The car works just fine without it, but won't pass emissions tests without it. I ended up not liking this mechanic much and moved to another one in the future.

I'm now trying to get the sensor replaced, but each time a new one is in it stops working. I'm going to a CarX with a good friend that works there. He is saying that the part is not after market and is a Benzo which is the part's manufacture I guess. Well he has put a new one in three times and after 10-20 miles the check engine comes back on for the same issue. He is thinking there is some kind of electrical issue so he had me take the car up to a dealership to get a diagnoses.

The dealership stated that they had to jump the car when I left it in their lot over night. They stated that I needed a new battery and the 02 sensor would actually cost $700 if I get it through them. They said that there are a few low voltage readings and that the battery no longer holds a charge. They stated that their course of action would be to put in a new battery and then a new 02 sensor. The battery issue is new to me. I have had no issues starting the car or it dying on me and this is a very cold area this time of year. I also do not have a garage so it's been outside overnight in the same temperatures without any issues in the morning. (I guess you can tell who I don't believe.) I will confess that the battery is at least 3 years old as I have not replaced it since getting the car so it could be the issue. I have had the CarX replace the battery and put a new 02 sensor in. The check engine light has come back on again. So the question is who is telling the truth and who do I trust?