Where is the o2 sensor in 2004 Chevy Malibu Classic?

[drive325mph]

I am just asking anyone that knows any mechanical knowledge. Does CHECK ENGINE light mean the o2 sensor or fuel filter is plugged up? The engine is running fine, but the light came on 3 days ago. So I just wanted to know where the o2 sensor is. What is the possibility that caused the CHECK ENGINE light to come on?

 

[cynthia]

The o2 sensor is somewhere in the exhaust system.

 

[myself]

Go to an autozone and have them test it to see a few vague possibilities, or pay the money and have a shop diagnose the problem.