Well I installed a high flow cat-converter in my cobalt not to long back.. My check engine light is always on, i believe because the car thinks that the stock cat has failed. Whenever i go for inspection, i just switch out the high flow, which is bolt on back to my stock cat. But in the future I want to install a hahn 3in full exhaust including the hi flow cat. Only problem is if i do that i cannot just throw on the stock cat for inspection because the stock cat is 2.5 inch.. How do i fix the check engine light, because i know its legal to have a high flow cat.. Do i need to install a performance o2 sensor?? PLzz Helpp!!

 

technically its not even legal to remove a factory emissions device unless it has failed but this is a quick fix with hptuners to disable the p0420 code

 

Go catless and erase the code and there you go, done deal.

 

i have an o2 angle adapter for the rear o2 sensor and i havent had a cel since... CTI 3inch dp with magnaflow hfc

get it on ebay 25 bucks

 

Isnt their a lil thing you can buy that hooks onto the car, finds the code, and erases it?

 

yes but the code will just come back after so many key turn cycles, the angled o2 bung or disabling the rear cat code in HPTuners are the only ways to get rid of it permanently

 

but if u disabel the second o2 code will the car still adujust the a/f mix right or is the a/f mix done with just the first o2 i had an svt foucs and i went to radio shack and and o2 sensor for the rear and the car thaught it was running prefect as far as a/f goes

 

FYI: No such thing as a "performance o2 sensor". How the car throws this code: If primary & secondary o2 sensor are showing same or very similar readings, with the cat being in between them, it shows it has failed with emissions control. With a functional cat, the o2 sensors will see different readings.

 

so which o2 sensor does the engine use to adjust a/f mix

 

the one in the exhaust manifold aka precat

 

ok so the second o2 just makes sure the cat is doing its job

 

exactly

 

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it think i rwmber seeing this on herre before but cna u use the second o2 hole for ur wide band or is best to put it closer to the header

 

You want it closer to the primary than in the location of the secondary ESPECIALLY if the DP is catted.

 

ok kool cuz i goiig to be gettin and headder and dp and was just wondering about that so i guess i will just have them put in the extra os bung for the wide band thanks

 

If your rear o2 is bad/cel'ing, I believe it can force the car into a predetermined afr, usually meaning rich, maybe even rich enough to damage engine or burn up a cat. Others have said it doesn't do anything, I'm just letting you know so you can investigate. I'd hate to see you mess up your car.

*I believe it's called a closed loop, something that should only happen until your engine reaches operating temp, but will continue with rear o2 issues, leading to problems? Someone correct me if I'm wrong, but I'm pretty sure that's what happened on my car, however I didn't have a scan guage on hand.

 

you can run the hahn catback on a stock downpipe as well

 

no my o2 is not bad every thing is fine im just wanting to get and headder and dp and do a wide band when i get my tax return lol and i was going to have some one on here thats lives close to me turn the second o2 off and tune the car for some 42 proble

 

But if your engine thinks your rear o2 is bad, my understanding is that it will do its closed loop beyond initial engine warmup.

 

ok but if i have it tuned and the second o2 turned off then the car will think the cat is doing its job and it wont go in to loop mode am i right or am i still missing something

 

you are correct

 

kooo; thanks ummm do u know any body close to the cleveland area that could do some good tuning for me

 

near ohio? i believe wicked is in the area

 

yah i am goingto school up here in celeveand ohio but my housae in morgontown wv so i dont have a garge up here in ohio so i was wondering if when i got mi 42 if i could take them to who ever is going to tune it for me and i could just put them in at there place and then they could tune it for me