There are 4. 2 infront of the cat and 2 behind the cat.


If they are bad they would toss a code, and the code would tell you which one of the 4 is bad. typically the ones infront of the cat have a rougher life.

I have a 2000 amigo with 83k and I'm getting about the same mpg as you. My MPG will go back up to 17-18 in the spring.....

It still won't hurt to change the front O2 sensors.