I went to Auto Zone to get the codes and they were:

*a/f ratio concern
*air leak near ho2s (heated oxygen sensor) bank 1
*ignition system concern
*faulty catalytic converter

The guy told me it was the o2 sensor.

I have a 98 Civic LX sedan. The only indcation I needed the codes read were the Check Engine light.

I've heard sensors are hard to find and cars have mutliple sensors. I'm certainly no mechanic so I assume its best to have a mechanic do this? And would I get the sensor from the mechanic or auto parts store? I think the guy said one is $65.

 

You probably have a crack in the manifold near the sensor. The DX / LX from 96 to 2000 all crack. Air coming in the crack causes bad readings from the sensor.

 

Oh really? Ok. Even if that's the case, I'd need a mechanic. I read somewhere else that the Auto Zone ppl can install the o2 sensor...but I'd think going to a mechanic is best. Unfortunately either way I'll probably be taken advantage of

 

Actually, if you can turn a socket wrench, you can swap out your O2 sensors pretty easily. I was just looking at the ones on my '97 LX the other day, and was marvelling at how easy they are to get to. Basically, it's open the hood, and look straight down. The first one (before the cat) is the metal piece with a wire on it that's coming from the middle of the exhaust. The second one (after the cat), is a short hand-reach down further into the engine bay.

If you opt to do it yourself, I'd highly recommend getting a socket designed for O2 sensors (looks like a deep-well socket with a slit in it for the wire. Simply follow the wire from the sensor to a harness, unplug it, then slip the socket wrench over the O2 sensor (let the wire come through the slit in the socket), and unscrew it. The new one gets screwed in, then plugged in, and you're done.

But, as mk378 pointed out, first check to make sure it's not something else.

 

Well I was talking to my dad and he is saying not to worry about it until emissions testing. Though I know if its the o2 sensor, and my fuel isn't mixing properly, it can harm the environment. And if it is the manifold, I know that has to do with directing the fuel and exhaust, so does that need immediate fixing?
Is it prudent to have a mechanic look at this or can it wait? I have not noticed any loss of mileage.

 

I would not just wait and leave your check engine light on, that is asking for your car to have more serious issues, unless you absolutly cannot afford to get work done and have no time to do it yourself.

replacing an O2 sensor takes 5 minutes. Replacing the header takes 30 minutes. (~seriously should not take much longer). My header is cracked but i dont have any of the issues you have. I would replace the O2 sensor and then see if you still have the CEL.

If O2 sensor doesnt fix problems then do a little more trouble shooting, after market headers are fairly cheap. You dont want your ride to start running lean, ect...

 

But the engine has more than one sensor so how would I know which to replace? Or is it both? And I think someone should look at it to see if the manifold is cracked.