O2 sensor

[millersmm76]

where is the O2 sensor located on a 2004 Honda Civic? Is it hard to replace?

[Killtodie]

There are two, one directly out the exhaust manifold another in the catalytic converter. The one in the cat might be hard to pull out, you will need a special tool to get out the one in the cat, otherwise a 21mm wrench will work.

 

Just soak it in PB Blaster and see if you can get them out, if your slim and your car isnt dropped, you can get underneath without jacking up the car.