Oxygeb Sensor

I'm A Shade Tree Mechanic. I Like To Do It Myself When I Can. I Have A 97 Aurora. Went To Autozone And They Scaned My Car And The Code Was For Oxygen Sensor. I've Looked Oxygen Sensors On Some Web. I Need To Know How Many Sensors There Are. I Beleive I've Located Two. One By The Catalictc Convertor(bad Spelling) And One Right Behind Radiator Off The Manifold. Any Help Would Be Greatly Appreciated

I think there are 4.

1. front left of engine(driver side)
2. rear of engine on top of exhause manifold
3. before cat converter
4. after cat converter

I think this changed somewhere in 97-98 year, but if memory serves correctly it went from 4-->3 in 98.

A clogged air filter can set an O2 code.