# Check Engine Light?



## koolkam89 (Dec 17, 2009)

Hello, I have a 2005 GTO and i have a question about the check engine light. Back in the beginning of the summer I took the exhaust off because I liked the loudness and drove it like that for 2 days, then put the exhaust back on. Ever since then, I've had the check engine light and then the reduced performance safety mode come on maybe 4 times. A few weeks after I put my stock exhaust back on I got a custom exhaust from the cat back. I was wondering if the change in back pressure could be causing the check engine light to come on? Thanks for your help.

Kameron

PS. Any good recommendations for a radar detector?


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## Mayhem5417 (Oct 18, 2009)

yea my cel is on too,,you can try a diagnostic at your nearest auto zone and they should tell you the source of the problem


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## jpalamar (Jul 22, 2008)

If you install long tubes or go catless, you will get a CEL. You need a tune to fix that. Shouldn't put your car in limp mode though.

Go to AutoZone and have then check what code is setting the CEL. It will help you trace your problem. With all the exhaust work you have had done, I wouldn't be surprised if it wasn't as simple as a bad front O2 or it just not being installed right.


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## Mayhem5417 (Oct 18, 2009)

jpalamar said:


> I wouldn't be surprised if it wasn't as simple as a bad front O2 or it just not being installed right.


not to steal the posters wanted help but when i checked a diagnostic at auto zone they told me it was something concerning the O2,,,when hearing that i automatically assumed it was because of my lack of cats,,should i still be concerned thats its something other than no cats


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## jpalamar (Jul 22, 2008)

Mayhem5417 said:


> not to steal the posters wanted help but when i checked a diagnostic at auto zone they told me it was something concerning the O2,,,when hearing that i automatically assumed it was because of my lack of cats,,should i still be concerned thats its something other than no cats


If it is the rear O2s, its because you need a tune to turn them off. Reason for the CEL is that without the cats burning the extra gases, your rear O2s will read an extremely high amount of emmissions, thus thinking the cats are bad. Tune it and you will make the CEl go away. If it is the front O2, it could be a number of things but typically your car will run like crap if they fail.

* note that there are O2s on both sides(duel exhaust) *


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## Mayhem5417 (Oct 18, 2009)

thanks a lot,,,see i dont need to drive 10 miles to autozone when i got cool GTO friends


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## perkGTOLS2 (Feb 1, 2010)

I have had this same thing happen twice in the last month and a half. after reading the owners manual and realizing the places i had fueled at have come to the conclusion that i had bad gas, safe mode went away both times after refueling with premium at the shell and then dumb me went and got gas the next time at the same place i did the first time and same thing happened half way through the tank. just threw som zmat fuel system cleaner and another refill at shell prob corrected and cel went off.


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