I think it was a 15097 - it's kind of long story but I'll give it to you:

I bought the car with whatever sensors were in it, but I immediately started chasing a P0133 code.

I bought a Bosch 15097 from FCP and put installed it in the front position. But I kept the sensor I took out, which I could tell was a bosch sensor and had the proper connector - so I guess let's assume it was a 15097 as well. The guy I bought it from (I sort of know him) told me he replaced the sensor the week before I bought it, and he thought it would take care of the code (but it didn't).

I continued to have problems with the code but had other things to chase down that actually could have been causing it, so I didn't look into O2 sensors again for nearly 2 years.

I eventually started to think everything /should/ have been cleared up but I was still getting the P0133, so I ran through the test procedure to test the O2 sensors and determined that the rear sensor was not behaving correctly.

I did some research and found out that the two sensors were the same, so I pulled the rear sensor and soldered in the sensor I pulled from the front position earlier. I assumed it was good based on the information from the seller that it was nearly new.

Now a question for you - is the sensor on the end of the 15097 more like the 15733 or more like the 15738?

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1998 V70 AWD->FWD->AWD Turbo 215k+