Prolly a dumb question but I've seen a lot of o2 sims go for 50$ shipped and o2 sensors can go for as much as 100$ shipped for the pair. I was wondering why doesnt evenyone just use o2 sims in the first place?

 

Because you can't use o2 simulators for the front o2's, only the rears.

 

o i c. well maybe for the rears then if you had to replace both your rear o2s for some reason. ok thnx.

 

I bought mine and then I ended up getting a mail tune and had the rear O2s deleted.

 

To add a bit more detail to the above correct response, OBD2 cars have O2 sensors pre and post cats to make sure the cats are operating properly. OBD1 only has them pre-cat.

Both OBD1 and OBD2 need the pre-cat for various aspects in the computer, but if you delete/gut your cat, the OBD2 cars will throw a light because the post-cat O2 sensor is picking up the fact that the cat isn't doing its job anymore.

So, the solution is to get a "sim" that fakes a signal from the post-cat sensors indicating correctly funcitoning cat on OBD2 cars so you can get rid of it. As already mentioned, the pre-cat O2s are needed in all cases.