02 sensor

I need to know if there are more than two sensors on my 2004 4.2 liter freestar. I changed two and still have a problem.:frown:

there are four. Two before each cat and two after each cat.

Thanks for the info. Now, where are the other two located if you know. I have looked under the car and don't see anything. As I said, I changed the one that is down front on the exaust pipe and the one just prior to the cat. I just don't see anymore.