Nickflo07

I have a 2000 civic ex sohc vtec. I just recent put aftermarket headers and exhaust. I bought a new primary o2 sensor because the exhaust system came off my old 98 and had to replace the o2 in to a correct spot. I drove the car for about 10 minutes and the bad o2 sensor reading came up. Can someone please tell me how to prevent this or let me in on a secret how to fix this.

CandyRedRC46

Which o2 sensor is the code for? Upstream or downstream? What kind of shape is your catalytic converter in?

Nickflo07

I don't really know. I took it to the auto parts store and the just told me the o2 sensor was bad. I had just replaced the upstream o2 sensor that same day. What explains the bog when I first take off?

Nickflo07

And I have a test pipe but looked like it has been welded before like.

CandyRedRC46

Well the down stream o2 sensor will cause a CEL if you do not have a healthy cat, but I don't think it would effect performance at all.

ek9_beast

I guarantee it's the downstream O2. Get a de fouler and that corrects the issue and removes cel.

Nickflo07

This is what i

ek9_beast

Yep. Get a defouler and that disappears. You aren't hurting the car by doing so

Nickflo07

Do I put it where the down stream o2 sensor?

rollinmyda

iTrader: (19)

Yes

ek9_beast

Yes downstream but get one with a 90degree angle or it will be hitting the underbody. With a 90 defouler it will run parallel to the exhaust

Nickflo07

Oh ok. And can you explain what this actually does? lol and I found a small leak where the weld is on the test pipe.

ek9_beast

What it does is make the O2 sensors read differently. Right now they are seeing similar flow letting the car know the cat isn't there or inefficient. It restricts flow to the downstream sensor. And no it doesn't affect any performance but does make the ecu happy and no cel

Nickflo07

Is that why these codes came up?

ek9_beast

100% yes. Defouler, defouler and defouler with a 90 in the downstream O2 slot and ur good to go

Nickflo07

Ok sweet! And I'm guessing I would have to order it online right? Not something I can pick up at a local auto parts store?

ek9_beast

Correct there's a guy on eBay I've bought 4 from and they're very nice quality but definitely not a retail stock item. If your exhaust is stainless make sure the defouler is stainless or it'll cause issues Down the road

Nickflo07

Yes it's stainless. Thanks for all the info.

ek9_beast

No problem