It's the one closet to the engine.
The oxygen sensor on a 2004 Honda Accord is found on the exhaust system. They are placed close to the catalytic converter so the sensors can properly read the exhaust flow.
Depending on which sensor, IS it sensor 1 or 2
In the glove box
Honda oxygen sensor is usually positioned in the exhaust manifold downpipe before the catalytic converter of your Honda vehicle or in the middle of the two mentioned components. For more details: http://sites.google.com/site/hondarepairsite/home/2004-honda-oxygen-sensor
where is the oxygen sensor in a 2004 astro van
Idle Air Temperature sensor.
The roof
I believe you'll find it at the point where the exhaust pipe fits into the inlet of the catalytic converter.
The 2004 Dodge Intrepid oxygen sensor can be found on the back of the air cleaner housing. Remove the wiring harness. Remove the oxygen sensor retaining screws. Reverse the process to install the new oxygen sensor.
First you need to know which one you are looking for. Your car has more than one oxygen sensor. Usually you'll have one in front of and one in back of the catalytic convertor and there may be one closer to the exhaust manifold as well.
You need to take a wrench to loosen the oxygen sensor, then you will need to disconnect the cord. Once you have done that you will then pull out the old oxygen sensor.
There are 2 oxygen sensors on my 2004. They are on the drivers side of the exhaust between the manifold and the catalytic converter. Put the vehicle up on ramps and duck under there and you will see them.