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2008 TrailblazerSS
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925 Posts
Discussion Starter · #1 ·
Hello Everyone!
This is the second time i have cleared these codes since i hacked off my muffler and straight piped it, otherwise the SS is completely stock, and I'm getting a check engine light for the rear O2 censor and its saying BOTH banks of my cats are bad...
Could this be due to the sensors being sensitive are set to have a certain amount of back pressure otherwise they think somethings wrong?

I mean I'm not worried about it because I'm about to slap on a set of headers and no cats but i just wanted you guys opinions to make sure i wasn't overlooking something that could be more serious.

So.... whatcha think?
 

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Premium Member
06 AWD SS
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4,200 Posts
I think you might be the first to throw a code just from a muffler delete. Personally I cut my factory muffler off and put a Magnaflow 11229 on it where the factory resonator is supposed to be and I never got a code. It's the standard mod on these things and the factory exhaust is only like 15% restrictive, something else is up with your truck. Maybe the increase flow is fouling your O2 sensors? Don't know, this is the first I've heard of that.:dunno:
 

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WANNABE SS OWNER
Trailblazer SS 2wd
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16,025 Posts
:iamwithstupid: I would check and make sure your O2s are still good.
 

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2008 TrailblazerSS
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925 Posts
Discussion Starter · #6 · (Edited)
I don't think they are unplugged.... at least i didn't unplug them ... ill have to check the O2 censors... How many total are there? on In or near each cat and one in the rear? or are there more?
And yea my MPG went down as well... but like you said its from me getting on it all the time to hear it roar ;)


Last time the code came up was last week... the exhaust mod was done over a month ago with no problems... so i took it over to autozone and they ran the free diagnostics thing for me and that's what came up. So i figured it was just confused censors and reset the ecu (unhooked battery then hooked it back up) and the codes went away....

Ill take a closer look this afternoon
 

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Premium Member
TrailblazerSS
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2,655 Posts
4 total O2's, 1 pre and post on each side. Maybe if your cats were already on the way out, flowing just a little more would be enough to make them say the cat is bad? Honestly I'd say it's just a coincidence, probably not related to the muffler swap.
 

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2008 TrailblazerSS
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925 Posts
Discussion Starter · #8 ·
Hmmm so you think the cats were already going bad before i did the Muffler delete? In that case if i took it to the dealership would they replace the cats under warranty?

When i get my headers in 2 weeks w/ no cats it shouldn't throw any codes right?

When i do the headers i am probably going to slap in a small magnaflow 4x9 or just do the turn down like I've seen a few on here.
 

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Premium Member
'07 awd
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2,422 Posts
What 02 sensor codes are you getting? Efficiency codes would mean bad cats.

If you install headers with out cats, you will get quite a few codes set, unless you have them tuned out.
 

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2008 TrailblazerSS
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925 Posts
Discussion Starter · #10 ·
What 02 sensor codes are you getting? Efficiency codes would mean bad cats.

If you install headers with out cats, you will get quite a few codes set, unless you have them tuned out.
Hmm, others have said they installed headers/no cats with no tune and had no problems and no codes...

Im looking to do the OBX longtubes/ No cats
 

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Premium Member
08 Black Granite
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4,004 Posts
What code in specific are you throwing?

I have a catted Y and still threw codes for o2's in-efficiency and slow switching. So yeah you'll be looking at a few until you get it tuned.

-But must be a coincidence like said never heard of a muffler delete throwing a code lol.
 

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TT AWD TBSS Jeep
TT AWD SS Pwrd Jeep
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5,825 Posts
Post the code numbers. But you may have one of those factory freaks, and you are outside of the 20% range the CPU can compensate for volumetric efficiency with the muffler delete. What mods have been done to the intake side?
 

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2008 TrailblazerSS
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925 Posts
Discussion Starter · #13 ·
No mods at all other than the muffler delete...
And i dont remember the codes exactly, i had them printed up the first time it showed up and not sure what i did with the little print out tickets...
they didnt print them this time...
ill run them again tomorrow morning and post the exact code numbers
 

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2008 TrailblazerSS
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925 Posts
Discussion Starter · #14 ·
OK so since the last time this is the only code that came up:

P0174 Bank 1 O2 Censor.

this code came up twice though...

Any ideas ?
 

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Premium Member
08 Black Granite
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4,004 Posts
That's a lean code, who told you sensor?

Clean your MAF and see it that remedies the code.
 

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Premium Member
TrailblazerSS
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7,324 Posts
if u eliminate the cats, you'll definitely get a CEL! i have a magnaflow high flow catted y on mine and i get p0420, p1133, and p1153 at least twice a week! either tune em out or deal with the light!
 

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2008 TrailblazerSS
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925 Posts
Discussion Starter · #17 ·
That's a lean code, who told you sensor?

Clean your MAF and see it that remedies the code.
Hmm.. Dude at Autozone said sensor...

Would just opening it up and spraying it down with some CRC maf cleaner suffice or is there a more detailed way to get it real clean?
 

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Premium Member
08 Black Granite
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4,004 Posts
I take it off the truck when cleaning MAF, no sense in sending that debris in to the intake. Just disconnect the NEG when cleaning that'll more then likely reset the code anyways then after the MAF is dry see it pops back on. It's prob. just an odd-ball intermittent deal. I've never heard of anything throwing a code after simply changing or eliminating a muffler LOL
 

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2008 TrailblazerSS
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925 Posts
Discussion Starter · #19 ·
Gotcha gotcha, Its drying now waiting to put it back on.
So your saying that's not even an O2 sensor Code?
So "lean code" you mean the MAF is just dirty and making it run lean?
:wtf:was autozone guy talking about? he must have been high.
 

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Premium Member
06 AWD SS
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4,200 Posts
It's Autozone, what do you expect? They told my fiancee that her low coolant in the reservoir was causing her check engine light to be on. Clean your MAF and maybe get a new filter in the process (couldn't hurt).
 
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