on thursday i changed out my above the cat o2 sensor after getting a CEL and taking it to Advance Auto to use their diagnostic machine. i was getting pretty cappy gass milageage and the car would idle funny, soi kinda figured that the o2 sensor would be the cause b/c nothing had been wrong with it b4. so i take out the sensor and look at it and it is crusted in carbon. i compared it to my new one and of course they both look different. so i decided to remove the o2 from below the cat, and it looked exactly like the one from above the cat. so now i am scratching my head and i decide to snap a few pics with my phone to see if anybody here would know anything about this.
anyway i cleaned off the below the cat o2 and istalled it and the new one i just bought and it has been running fine. but i am still wondering what the hell the difference is between the two. in the 1st pic the one to the left is the below the cato2 the one in the middle is the old above cat o2 and the one on the right is the new one. second and third pic is the new and old one before i replaced.

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those pictures are too small to see anything.


what year is your car?


and what did the diagnostic machine tell you? did it actually say bad O2 sensor? what was the code?

 

i have a 97 DX 5spd coupe. i already threw the paper away that i got from the guy at advance auto. but the message said it was running lean. the machine he used was a little hand held device that plugs in somewhere in the area under the steering wheelright about where someones knees would go if you were sitting in the seat. i will see if i can make the picture bigger.
my civicwas getting maybe 20 mpg (highway) before i changed it out and now it is back to about 35 mpg.

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