oxygen sensor

My service engine light came on, so I took it to a parts store to be checked. They said I needed an Oxygen Sensor but they failed to tell me which one. How can I find this out? Do I need to take it back to that parts store or should I take it to a shop to find out which one I need.

Take it to a shop, Unless you can afford to replace both, just in case

Chances are good it's the first one, the one on the manifold. The second one is just there to make sure the cat is doing somthing, but the first one controls how well the car runs and gas milage.
I assume you have a 96 or newer Escort?

:screwy: MY CHECK ENGINE LIGHT HAS BEEN ON FOR 2 YEARS NOW.....i GUESS I WILL ASK THEM TO CHECK it out in the morning, :uhoh: I have been having some shake rattle and roll ( trying to die) over the weekend and I am cursed with cars.....always have bad luck!! I also hear a roaring noise when the windows are down on this car???????and going thru brakes like water......gosh just had em put on at the begining of the year and already need em???? I dont ride my brakes either.....