Custom exhaust causing p0420

[NickTej22]

I recently got a custom made catback, I believe it is 3 inch pipe, possibly 2.5, with a resonator and a tip. ($80 fix for a rotted out setup). Anyways after that I'm getting a code for o2 sensor bank 1 sensor 2, and they only have 2 sensors(unless California emissions equipped). Doing some reading I found i'm not the only to get this code so it's likely the exhaust causing it.

 

My questions are

1. does this mess with performance, since my car occasionally stalls on me?

2. is there a screw in bung or a way to trick this without getting the CEL?

[wpgspecb]

are you running a downpipe ? Cobb accessport ?

 

I thought both o2 sensors are before the midpipe, therefore the "catback" shouldnt affect anything before it.

 

What year car, mods?

[NickTej22]

OH CRAP, sorry man. It's a n/a 95 legacy brighton 2.2

[MDKSDMF]

Is it a lean code perhaps?

[NickTej22]

I have a custom catback put on, I am pretty sure that's why. Not worried about it since the last sensor does nothing to performance, just reads.

[MDKSDMF]

BUT that code could be adjusting timing and other stuff that could be holding your car back. But since where u modified has nothing to do with the 02 sensors you should be safe. get the code read tho and tell us what it is

[fahr_side]

P0420 is just the rear cat sensing very little difference in oxygen content from the first one, before the cat. That says the cat isn't working correctly or is missing, it doesn't change your fueling, pull timing or anything else. It's purely emissions related. Sure you didn't touch the cat section? Do you have a leak somewhere?

Yes, you can buy a sensor extender to pull it out of the exhaust stream. It sometimes works. I'd look for the leaks or missing cats first.

[NickTej22]

The exhaust was just done. Not sure how long the p0420 code was on because the previous owner pulled the bulb out of the cel light on the gauge. But While we were under the car we noticed the whole front end of the exhaust looked new. We didn't screw with the cats or anything. Everything seems ok.

[NickTej22]

Where can I get a bung extension?

[MDKSDMF]

ya but far side is right. if u have a precat leak u could get a lean condition. id check out ur cat and leaks

[NickTej22]

I don't have any exhaust leaks. They were all fixed at the exhaust shop. Only thing is the catback, its a 2.5 or 3 inch pipe with no muffler, just resonator.

[fahr_side]

Most likely your rear O2 sensor is borked. Like I said, it doesn't do anything except check the cats are doing their job. If you can swap sensors with a car with a known good sensor to confirm yours is bad, all the better. O2 sensors are kind of expensive, can fail in a variety of ways, and are impossible to test.

If your cats are dud, you can space the sensor with a CEL eliminator (lots of places sell those), replace the sensor or the cats.

[MDKSDMF]

cant you also protune around the code?

[fahr_side]

cant you also protune around the code?

Pretty sure from the age of the vehicle that it has the JECS ECU which is not supported or defined by ECUflash or AP. I know the devil had an interface to reflash turbo ECUs of this vintage, but AFAIK they hadn't bothered with the n/a models.

By 'the devil' I of course mean Ecutek.