I have been researching alternatives to OEM sensors and found a couple of interesting things: all Bosch universal sensor that local store sells are different in size and exsposure of the actual sensing element. It directly affects how well it measures. Secondly you have to check if you car has an air pump and if you do, I believe you are out of luck and will have to buy OEM one. Check for it under driver's side headlight, you will see hoses go into electrical pump. They claim air pump on cold starts affects mixture so that it may skew your non-OEM O2 sensor measurement. (I am not quite sure how it affects it, air pump was design to keep mixture leaner and exaust cleaner on start, I will appreciate if Volvo techs speak to that).

Anyway, right now I am sitting on a fence, my car is 1994 and though it doesn't register a code it doesn't give me a very good mileage and some posts say that it is a good idea to replace front sensor at 60K. Is that true?

Hope that helps,

D.