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I have a Pontiac G6 2008 4cyl and I just recently started having an issue with the car not accelerating like it use to. The CEL came on and indicated a P0420 code so the first thing I checked was my O2 sensors and ended up changing out the up-stream sensor, the downsteam was fine. I reset the code in the car and the CEL went off for about a day, but there was little improvement to my car. The next day the CEL came back on and the car seemed like it was worse. Took it to get the CEL code checked and the same P0420 code came up and the person told me it may be my catalytic converter. Since the catalytic converter is covered under warranty for 8 years or 80K miles I took it to the GM dealership and they said they couldn't figure out what was wrong with the car. He said everytime a code came up and he checked it the code would immediately clear itself out...basically it was misfiring. He said they hit the catalytic converter to see if there were any loose pieces or to see if they heard a hollow sound that would indicate it was clogged and they didn't get any indication that anything was wrong with the converter. I dont loose any gas mileage and i dont have a wet floor or the rotten egg smell that I have seen alot of people say they have had when theirs went bad. The dealership told me that since I have an after market alarm system (viper) I need to completely remove that and see if the problem is fixed. He said since the alarm system is hard wired into my cars computer it could be causing mis fires. Is there anyone who has had problems with their G6 like this or any insight on what the problem may be? This is starting to get expensive and it sucks that the dealership cant even figure out whats wrong but has no problem charging me and telling me they dont know whats going on!!! :mad:
 

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I'd say it's the cat. I was running with a p0430 (bank 2) code for a while. I'd clear it and it would come back. I switched around 02 sensors and it still came back. Finally I got a new cat and problem solved. Hasn't come back yet.
 

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you drive a 6 base model with 4cyl...its supposed to be like that ;)
 

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My car was never like this before! i know I have the basic model but its sluggish to the point where its stalls when i press the gas and takes 15 secs to even gain a little speed. Then as soon as I have to stop it repeats the same problem. im pretty sure its the catalytic converter but i was wondering if anyone else heard of aftermarket alarms short circuiting the g6 computer and causing misfires??
 

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I have a Pontiac G6 2008 4cyl and I just recently started having an issue with the car not accelerating like it use to. The CEL came on and indicated a P0420 code so the first thing I checked was my O2 sensors and ended up changing out the up-stream sensor, the downsteam was fine. I reset the code in the car and the CEL went off for about a day, but there was little improvement to my car. The next day the CEL came back on and the car seemed like it was worse. Took it to get the CEL code checked and the same P0420 code came up and the person told me it may be my catalytic converter. Since the catalytic converter is covered under warranty for 8 years or 80K miles I took it to the GM dealership and they said they couldn't figure out what was wrong with the car. He said everytime a code came up and he checked it the code would immediately clear itself out...basically it was misfiring. He said they hit the catalytic converter to see if there were any loose pieces or to see if they heard a hollow sound that would indicate it was clogged and they didn't get any indication that anything was wrong with the converter. I dont loose any gas mileage and i dont have a wet floor or the rotten egg smell that I have seen alot of people say they have had when theirs went bad. The dealership told me that since I have an after market alarm system (viper) I need to completely remove that and see if the problem is fixed. He said since the alarm system is hard wired into my cars computer it could be causing mis fires. Is there anyone who has had problems with their G6 like this or any insight on what the problem may be? This is starting to get expensive and it sucks that the dealership cant even figure out whats wrong but has no problem charging me and telling me they dont know whats going on!!! :mad:
Mileage? The 420 is almost always the bank 1 cat (I've learned to avoid absolutes). The question is has is worn out or been destoyed by running with a rich fuel trim due to another issue. No other DTC's? How do you know it's misfiring?
From your paragraph I got the feeling that dealer is not interested in fulfilling the emissions warranty. Maybe he wants to wait you out. You may need to try another dealer or take it up with GM corporate.
 

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...I took it to the GM dealership and they said they couldn't figure out what was wrong with the car. He said everytime a code came up and he checked it the code would immediately clear itself out...basically it was misfiring...
That is total bulls++t. DTC's dont come & go on a lark. It requires a number of driving cycles without the original conditions that set the code. The number depends entirely on which code is set. You're being played for a fool. Unfortunately, because you have that aftermarket alarm, he has a perfect get out of jail free card to play.
One more thing: tapping on a cat is not a way to test if its bad (unless its really been totally destroyed).
 

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Discussion Starter #7
Yeah, Im taking it to my dealership now. I didnt want to at first cause my car was so bad i didnt want to make the drive because of the way the car is acting but its the only dealership i will trust at the moment. Yeah the guy at the first dealership was full of crap, i have never heard of codes coming up and then clearing themselves and my alarm system is way to expensive to take off and there is absolutely no guarentee it will fix the problem. I told my dealership straight up that the better take the catalytic converter off and look at it or im not paying for anything reguarding service, if its not the converter im ok for paying the 65 dollar charge but they better not give me the same bs the first dealership did and say the need to have a code show up or they dont know whats wrong. We will see how it goes cause im about ready to just get rid of this car and get something else but this is the only prob the car has had its just dealing with the dealerships that is upsetting me. Thank you all for your input:)
 

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Since you haven't stated the mileage all I can assume is that its under 80K. That cat did not die of old age. More than likely an overly-rich fuel trim destoyed it. Unburned hydrocarbon fuel hits the very hot cat & creates a fire which overheats the catalyst literally incinerating it. One thing that allows unburned fuel into the cat is a misfiring cylinder. A cylinder that does not fire forces unburned fuel into the exhaust. In other words, the bad cat is a symptom of something else (that may have been repaired already-I have no way of knowing).
 

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my car gets seriously! and i mean seriously! hot underneath to the point i cant stand next to the car in shorts...could this be cat related? i also get a check engine light shortly after starting the car cold half way to its heated position at 225 ....any ideas?
 

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^ Get the check engine light checked out so you know where to start. most auto parts stores will scan it for free.
i did, they told me it was a cylinder 3 misfire. they then replaced wires and plugs..a few filters bunch of small shit...none of it got rid of the check engine light flashing...so they informed me the only thing it could be is (and i believe this is what the called it...but i do know for sure it was a coil they mentioned) they called it the engine coil and that if i didnt replace it my engine would eventually melt. they told me this part would be 1500...

i never replaced it...i still get the check engine light every now and then.
but my engine hasnt melted yet
 
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