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post #1 of 5 (permalink) Old 04-29-2013, 02:11 PM Thread Starter
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Question Header & Engine Code;

Well I ordered my header and my o2 bung plug today but that's not the point well I got a code po420 & uo121 and a mechanic told me to change the o2 sensor and to start using premiem gas?? I do know that as of now there's a exhaust leak but will be sealed when I put the header on but will that fix the issue?
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post #2 of 5 (permalink) Old 04-29-2013, 04:38 PM
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Well, the p0420 is an 02 sensor for sure, but thats an after cat sensor DTC. Its sensing from the before 02 through the cat-converter to the rear 02. The rear 02 is either the issue or your cat is toast. The u0121 is a manufacturer issue and not a powertrain (p=powertrain, u=unibody).

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post #3 of 5 (permalink) Old 04-29-2013, 04:55 PM Thread Starter
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Brand new dp so its not fried just the o2 sensor and does the uo121 matter?

---------- Post added at 07:55 PM ---------- Previous post was at 07:54 PM ----------

What about gas grade?
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post #4 of 5 (permalink) Old 04-29-2013, 09:22 PM Thread Starter
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Are all o2 sensor for all cobalts the same fit? Cause I could a new o2 sensor on eBay for 27 plus free shipping and it says its compatible with all cobalts and I just wanna make sure it fits?

---------- Post added at 12:22 AM ---------- Previous post was at 12:18 AM ----------

Here's the o2 sensor...

http://item.mobileweb.ebay.com/viewi...id=89380114816
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post #5 of 5 (permalink) Old 04-30-2013, 06:31 AM
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you would probably be the first one here trying here. I got a Denso sensor and it works fine.

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