Hi all Once again I need your help. The middle part of my civic's exhaust has a hair thin crack and it is starting to make some noise. The thing is, there is something connected with a wire to the exhaust and I don't know the name of it and what it does, please see the picture, it has a red circle around it. I would like to change the exhaust myself as I did another day with the rear box of the exhaust, but I would like to know what kind of care I should take with this thing while replacing the exhaust. Any help will be appreciated.

 

That looks like your o2 sensor.

Its for emissions, its important to keep that in your car unless your taking you car off the road for racing purpose.

There are tools to remove this, or you could just use wrench.... might take a bit longer but it will work.

From the o2 sensor the wire leads back to the car, there should be a clip, unclip and then you can remover your exhaust with the sensor in.

 

Thanks you for your prompt reply
The reason I think I need to take the secondary 02 sensor out is to replace the middle box of the exhaust because it is the place where I have a crack. To be honest, I took this picture when I replaced the rear exhaust but I didn't looked properly how many parts this middle section of the exhaust is made of. I know there are one box and the cat. I thought they are all together in one piece, replacing the middle box, I thought I need to replace the cat as well. As I said I haven't lifted the car yet to have a proper look.
Does the secondary 02 sensor come together when you buy a new cat or not really?

 

that box you keep referring to is your Catalytic converter. converters are a good amount of money to replace.you could just have the crack welded if the cat is still good. as for the 02 sensor for your year and model it probably cost more then $40 dollars. if you remove the cat all together then you will never pass emissions or smog test.there sold separately and only use NTK or DENSO sensors.

 

Hi again
Today I managed time to lift up the car and I took another picture. It is marked in red where the crack is. I had the car in the garage twice to weld it up and ends up cracking somewhere around where it was welded last time. So I don't want to spend more money welding up that box. While the car was up, I had a proper look at the exhaust pipe that comes from that box to the cat, you guys are right, there are 3 bolts but because they are kind of hidden within the cat's shield I never noticed these 3 bolts. They are pretty rusty and also are the bolts of the shield, so good luck on me to remove them.
Probably one day before I change the box I will put a bit of WD-40 to help. I wonder if there is any gasket between the cat and the pipe where the bolts are?
Thanks for your help.

 

The part that is leaking is the resonator. You would replace the whole "B pipe" which bolts on to the back of the cat and goes back to the rear wheel area where it bolts on to the muffler and tailpipe assembly. You do not need to do anything with the sensor, it stays put while you take the pipe off of the back end of the cat.

 

As I find out nothing to do with the sensor. I will prepare my blow torch for the bolts. They are really rusty.

 

im not sure why you keep referring to it as a box when its cylindrical ?? but anyway parts numbers #18 #25 and #19 since you'll most likely need new gaskets also since you failed to mention make and model this is for a 98 EX Honda Automotive Parts also they have the bolts if you need new ones. you are also most likely going to need new spring bolts numbers #21 #22 but you can find those at any local parts store.

 

Yes I know it is cylindrical. Here where I live many guys call it box, that's why I ended up calling it box.
It is a civic 6 gen 1.4 sport from 2000

 

were i come from slang for "box" refers to a womens lady bits. also we refer to the resonator as a resonator.