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Discussion Starter #1 (Edited)
Hi everyone! So I know the cats on these cars can have problems. I have replaced both catalytic converters on my 05 G6 Base within the past 8 months. The first one I replaced maybe last July or August. The second one I had replaced in January. Now it is April and I am having some power problems. Car won't get past 60 on highway. A friend (not a mechanic) suggested transmission issue.

I went to a local shop and they told me the Downstream 02 sensor is bad. They say that replacing just the 02 sensor most likely won't solve the power issue because when the 02 sensor is bad, it means the cat is bad. They said it looks like I have "pull-a-part" type parts down there and I would need to replace the whole downstream cat. Mind you, I got both cats from O'Reillys because the shop who did the labor didn't have the cats available.

Now, my questions are:

1. Do you think a cat would go bad in just 2 or 8 months?
2. Should I just replace the 02 sensor in order to fix the power issue?

Thanks in advanced!
 

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Discussion Starter #3 (Edited)
They said p0430. I just dont understand this because I changed out both cats recently. They told me their aftermarket cat will cost about $1000.00. They suggested though that i get one from the dealer. The parts at OReilleys costed about 350-400 each. *Sigh*
 

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DTC P0430 Catalyst System Low Efficiency Bank 2


What is your current mileage?
What were the original symptoms/codes that were occuring that led you to replace the first cat?
What were the original symptoms/codes that were occuring that led you to replace the second cat?
The only code currently popping is the p0430 & the ONLY symptom is "Car won't get past 60 on highway"?
More details are much better than less.

1. Do you think a cat would go bad in just 2 or 8 months?

Only if bank 2 cylinder/s had been misfiring for quite awhile. You would have noticed something.

2. Should I just replace the 02 sensor in order to fix the power issue?

If you are over 100K, I would replace all four sensors as they get lazy with age.
 

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Discussion Starter #5 (Edited)
DTC P0430 Catalyst System Low Efficiency Bank 2


What is your current mileage?
What were the original symptoms/codes that were occuring that led you to replace the first cat?
What were the original symptoms/codes that were occuring that led you to replace the second cat?
The only code currently popping is the p0430 & the ONLY symptom is "Car won't get past 60 on highway"?
More details are much better than less.

1. Do you think a cat would go bad in just 2 or 8 months?

Only if bank 2 cylinder/s had been misfiring for quite awhile. You would have noticed something.

2. Should I just replace the 02 sensor in order to fix the power issue?

If you are over 100K, I would replace all four sensors as they get lazy with age.
Current Mileage: 150K

What were the original symptoms/codes that were occuring that led you to replace the first cat?:

The original symptoms were extreme loss of power to the point where it could not even move past 10 - 15 miles per hour...crawled up hills...weird rattling sound, also car jerked around a lot with rpms moving up and down while idling. Pressing gas resulted in extreme power loss. You cold see the mph lever actually move way down. Diagnosed as bad cat and multiple misfires. I had to replace the cat along with the spark plugs and wires. Code I believe was P0420 and P0300. They said I should replace the second cat too, but I didn't have the money until months later.

What were the original symptoms/codes that were occurring that led you to replace the second cat?

The original codes/symptoms were again extreme loss of power...couldn't get past 20 or 30 mph. Pressing gas pedal led to decrease in power. I knew from the first experience that I needed to replace the second cat, which I already had laying around the house. I had bought it previously, but never had it installed. Once I had it installed, problem went away. Car drove just fine. This was back in late January.

***I don't think the O2 sensors were replaced when I replaced these cats (unless they come with the cat which I don't believe to be true) because I didn't purchase new ones. So, that would mean they are the same old O2 sensors on both new cats.***

The only code currently popping up is the p0430 & the ONLY symptom is "Car won't get past 60 on highway"?:

Yes, that is the ONLY symptom and ONLY code they are pulling. Otherwise the car drives fine. There is no decrease in power when gas is pressed. The local shop that I most recently brought it to stated that just replacing the 02 sensors most likely will not resolve the "can't get past 60" problem.

More details: My problem feels like this...when I first got the car, I could step on the gas half way and it would accelerate fast. When I floored the gas, it would accelerate really fast...I was like "wow, this car is pretty damn fast!" Now, I step on the gas half way and it barely has a response. It does get a bit faster, but not by much at all. I have to stay in the right lane and drive like an old lady. BTW, I am not an aggressive driver. I don't accelerate hard after a stop. I am usually in the left lane going about 70 - 75. I might even go 80, but that is my limit.
 

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Considering the mileage, I'd replace all four O2 sensors. While replacing the sensors, have an exhaust backpressure test done on bank 2. That will tell you if the bank 2 cat is clogged (though I seriously doubt that it is). Don't let them talk you into replacing a good cat.

Have you ever noticed the check engine lamp flashing (indicating a high misfire rate)? You may have another issue that is causing misfiring (which can destroy cats).
 

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Discussion Starter #7
greenman, thanks so much for your advice. I really appreciate it. I called the shop today and I asked them to quote me on four 02 sensors and I let them know that I had never replaced the sensors when I got my new cats. They said, "Well, the code you got is for catalytic converter...it indicates that it is bad, so you should call O'Reillys to see if there is a warranty on the part." I'm like, "Ok." *sigh* I asked the guy if they were sure it is definitely the cat, considering I never got the o2 sensors replaced. They said, they are going to go off of what their tech is telling them.

No, I am not experiencing the CEL flashing. This was happening when I got the first cat replaced. It was flashing like there was no tomorrow every time I accelerated. That is when I was having misfires. The shop did not see any misfires this time around. They did a diagnostic on the car (cost $100.00) and the P0430 was the only code pulled. Who should I go to for the backpressure test? Will they (Firestone) do one for me? I wonder how much it will cost...wish I had my own mechanic.
 

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Discussion Starter #8
One other tidbit. About a month and a half ago, I was getting another CEL code...P0128...something about coolant or thermostat. Then the CEL light turned off. When I brought it to the shop two weeks ago (with the light off), they did a diagnostic and did not find anything wrong with the thermostat or coolant (which I specifically asked them to check on). In fact, they could find absolutely NOTHING wrong with the car. I had asked them to check on anything that could cause a slight decrease in power. Again, they found nothing wrong with it after spending an hour in diagnostics.

Then I brought it back this past Saturday when I noticed the CEL came back on. Then and only then were they able to find something wrong based on the P0430 code. I asked again if they saw anything wrong with the thermostat...was it stuck in an open or closed position? They said there is nothing wrong with it and they are not pulling that P0128 code. They are only pulling the below threshold code and are insisting on replacing the cat. I thought that was weird and wonder if they could be related.

*confused*
 

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I called the shop today and I asked them to quote me on four 02 sensors and I let them know that I had never replaced the sensors when I got my new cats. They said, "Well, the code you got is for catalytic converter...it indicates that it is bad, so you should call O'Reillys to see if there is a warranty on the part." I'm like, "Ok." *sigh* I asked the guy if they were sure it is definitely the cat, considering I never got the o2 sensors replaced. They said, they are going to go off of what their tech is telling them.
If the mechanic put it on his scan tool & found that the post-cat O2 sensor was fluctuating up & down like the pre-cat sensor, that would also be good evidence that cat has gone bad. But I have no idea if he did that. If it has gone bad, then you either have an engine problem that is destroying the cats or that VERY rare cat with a manufacturing defect.

No, I am not experiencing the CEL flashing. This was happening when I got the first cat replaced. It was flashing like there was no tomorrow every time I accelerated. That is when I was having misfires. The shop did not see any misfires this time around. They did a diagnostic on the car (cost $100.00) and the P0430 was the only code pulled. Who should I go to for the backpressure test? Will they (Firestone) do one for me? I wonder how much it will cost...wish I had my own mechanic.
I'd stick with whomever replaced the bank 2 cat. I feel your pain having to rely on the honesty of repair shops.

FWIW, if the CEL ever flashes on any car, turn off the engine immediately & have it towed to a shop.
 

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One other tidbit. About a month and a half ago, I was getting another CEL code...P0128...something about coolant or thermostat. Then the CEL light turned off. When I brought it to the shop two weeks ago (with the light off), they did a diagnostic and did not find anything wrong with the thermostat or coolant (which I specifically asked them to check on). In fact, they could find absolutely NOTHING wrong with the car. I had asked them to check on anything that could cause a slight decrease in power. Again, they found nothing wrong with it after spending an hour in diagnostics.
The 128 code essentially means the engine was not heating up normally. There are several possible causes. Considering the mileage & the 128 code, I'd replace the engine thermostat unless you know it's already been replaced recently.

Then I brought it back this past Saturday when I noticed the CEL came back on. Then and only then were they able to find something wrong based on the P0430 code. I asked again if they saw anything wrong with the thermostat...was it stuck in an open or closed position? They said there is nothing wrong with it and they are not pulling that P0128 code. They are only pulling the below threshold code and are insisting on replacing the cat. I thought that was weird and wonder if they could be related.
Does not sound like it's related, given your description.
 

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Discussion Starter #12
I haven't had the MAF sensor or throttle body cleaned. I've had the car about a year. All I know is that it had clean car fax/autocheck reports and checked out fine when I had a mechanic look at it prior to purchase. I bought it with 127K miles on it.

I will have them replace the thermostat.

I did speak with another mechanic who came very highly recommended. He said that all cats have a warranty for 2 years or 24K miles. He said I should call up O'Reillys. He will also take a look at the car and give me a (free) thorough diagnostic of any work that needs to be done on Monday.

He said the code most likely means a bad cat, but he will take a look at it. I will keep you updated! :)
 

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How Many 02 Sensors??

I just can't seem to find anything to really tell me for sure?? I have 2007 GT 3.5L. How many do I have?? I have looked online and it seems that I can get 3 different ones which leads me to believe there is 3 but I have read that there are 4?? Have my CEL on again and looking to start cheep before replacing the cat.
 

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I just can't seem to find anything to really tell me for sure?? I have 2007 GT 3.5L. How many do I have?? I have looked online and it seems that I can get 3 different ones which leads me to believe there is 3 but I have read that there are 4?? Have my CEL on again and looking to start cheep before replacing the cat.
There are 4 O2 sensors on a 3.5l. The base cat warranty is 8/80 but was extended for some VINs (can't remember the details). Dealer will know. The post-cat sensors only serve to check catalyst efficiency & play no role in fuel delivery.
 

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Thanks for the help!! Think my G6 is feeling a little left out cause I have been putting some money into my wife's van for like 2 weeks now. Lol!! Almost at 180K so I would not be suprised if it was the cat but hoping that replacing the original o2 sensors will fix it. Will see though?? Let you know what happens. Thanks again!
 
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