2003 WRX stock. Threw the 'ol P0420 code and decided to change the rear O2 sensor. Problem is, not too much info on the rear one. A bunch of install stuff but not much on the sensor itself. So, I bought this one. Drove 80 miles, code is back.

My question is, did I get the wrong one? Does it matter?

I saw a tutorial on changing the front one and the guy used this one. Would that be a better replacement?

 

They look exactly the same, but the part numbers and prices are radically different.

I'd say write both part numbers down, then google them to see what fits them, or ask o'reilly's themselves and ask what the difference is.

Also, are you sure its not just an old cat? Either your o2's bad, cat's bad, or you have a modified exhaust system(impossible in your case)