After having this car for almost a year, I thought I fixed every problem and code I bought it with.
Last fix was going back to stock intake from eBay and new Bank 1 O2 Sensor (NGK).

Now I get a P0420 irregularly. I thought it was because of the warm ass weather we're having in MI. It's 92F right now.

I got the code again when I pulled into my driveway from work today along with a P0300, but that's the first time I ever seen that code on my car ever.
I have never got a P0420 either until going back to stock and replacing my O2 Sensor.

I've just been clearing it, but obviously theres some sort of problem that isn't full blown yet.
Any suggestions where to start first?

 

Ain't 420 low cat effiency? Paired with random misfire. I would say if u have replaced urno2 sensor that your cat is taking a ****. Replace with aftermarket and disable the code 420

 

That would just require a new down pipe, would it not?
I'll probably just find a stock one on the classifieds, as I'm down with mods on this car, and focusing on my bike.
I wouldn't need to disable the code though after I did replace the cat/dp just clear it, right?

 

would need to clear it with an interceptor or pull the battery conn a few mins. how many miles? i think they have to give you a new cat up to xx,xxx miles or w/e. your o2 sensor isn't bad, p0420 means the rear is reading too close to the front aka cat not doing its job.

 

I have a Scan tool. 154k.
My O2 sensor WAS bad. I had a P0132. I was just giving information before the problem occurred.

 

p0420 is low cat efficiency. If you've already got a stock downpipe in, just swap another stocker on and it should be fine. If you've got an aftermarket downpipe, that's what's causing it, catted or not

 

ya my bad i read it wrong like you were gonna buy a rear one to fix it for some reason

 

It's been stock for the life of the car, and at 154k miles I'm not surprised its on its way out.
My happiness was short lived since I thought I had everything fixed for awhile.
Ah well.. At least I got paid today.

Is there a reason it's intermittent though?
I can go a couple days just fine, then randomly it'll come.
Weird now since the car can run in a closed loop the cat wants to go out.

 

Yes. Depednds on how your driving and diff temps equal diff air density which equals different complete combinations percentages. Which means more or less unburnt fuel going thru cat.

 

Makes sense. Not to mention my exhaust sounds a little raspier. Not full blown out cat raspy, but downshifts and coasts definitely have more sound to it. Of course, that could be a placebo since I didn't know exactly what was going on.

 

hey i'm getting this code now too, just installed a zzp longtube catted header paired with my stock catback. does this mean the 02 sensor just doesn't adjust well with this setup or what? oh and it popped on a few days AFTER i installed. can i just get it tuned out? planning on getting tuned soon

 

It just means that the aftermarket cat isn't performing up to the ecu's "standards". Yes you can just get it tuned out, just mention it to your tuner

 

I have a stock downpipe with 55k on it that has a broken flex section. you can have it for like 20 bucks, and I think a muffler shop will probably weld on a new flex section for around 100 bucks. would be a lot cheaper than buying a new one.

 

Like Tommy said. The cat is a high flow one from ZZP, so theres more air passing through compared to the stock one. Post cat o2 sees it as "below efficnecy" because of the increased air leaving the exhaust.

Either get a o2 defouler or get it tuned out.

And thanks Saber, but this thread is a bit old and I actually just picked up a stock dp on here a couple weeks ago and fixed everything up.

 

i think 420 might stand for to much weed smoke in the car...lmao