Thread: Removing the Rear O2 Sensor and Getting Rid of the CEL

I installed cat back system, and well having a 99 Sentra, I have the extra long Cat. So it's making the whole cat back piping be pushed back more, thus not really sitting in place etc.

I was thinking about either getting a < 98 cat or a test pipe. If I go with a test pipe, I will be harming the nature, wont give me any gains because the stock cat doesn't cause a significant amount of back pressure.

One of the main reasons I don't want to bother with a test pipe is because of the CEL and not having the Rear O2 sensor might cause bad mileage or some other crap.

Which brings me to my question, I guess I should pack up my stuff and go to Bel Air....

But seriously... whats the real purpose of the Rear 02 Sensor?

EDIT: Changing the name of this thread to more of what it has become
Removing the Rear O2 Sensor and Getting Rid of the CEL

I think the ECU uses it in combination with the front to gain a more accurate idea of your A/F ??

nope, its there to verify that the cat is working. if the readings between the two sensors are wildly crazy then it knows something is up, like if they are the same then the cat isnt working

Just an FYI, the 95-97 cats have a skinny O2 sensor, whereas the later 98-99 cats have a fat O2 sensor. It's pretty easy to use a 98-99 cat in a 95-97 with an O2 sensor adapter (using the original skinny sensor), but you run into problems the other way around.

There's no way to use the fat sensor in the skinny hole. You would need to rewire it and that appears to be a challenge as well. The fat O2 is 3 wires and the skinny is just 2. If you can live with the code (no testing), you can just plug it up. The cat would still work just fine. You can take out the bulb so the CEL isn't always on.

I forgot something.

Really I would recommend shortening the exhaust. That's the easiest option.

Yeah it just checks the cat is working, without it you`ll get a CEL...this wont effect how your engine runs though.

Thanks for the replies guys! I was thinking about maybe getting a test pipe, and just dangling the O2 sensor someplace, but if it checks for differences then it will throw a CEL lol...

Swiss, I remember your thread , but didn't know that there are not enough wires on there

I wonder if I can take the Test Pipe and drill a hole for the O2 sensor... hehe

And here is why I want to replace my stock cat btw...






It's nice and rusty, and it looks like the netting inside the cat is ribbing

Bah... Just run that open head... The cool air through the radiator will go straight to the exhaust ports and cool the exhaust gases = more power...

Dang it, I'm not on the old forum anymore...

I would suggest seeing if Fred or Mikos has a stock cat you can buy... Remember to have it marked as scrap metal when shipping... Don't ask me how I know...

Cheers-

Dang I should try that! Who cares about Carbon Monoxide in the car!

The idea of using a stock cat kinda goes out the window because of the O2 sensors...

A crazy idea just hit me... ok say I replace the cat with the Test Pipe.

Then I take the O2 sensor, and make an extender... to reach the hole on the Downpipe...



Do you guys think that would keep me from getting a CEL?