Thread: Need help with 0420 and 0128 code!!

Ok thanks. I think when I looked at the live data I did see the upstream sensor readings fluctuate but I also think the downstream were fluctuating also but not as much as the upstream o2. Its just hard to believe that my CAT is bad again becuz it was just replaced by the dealer under warranty about 2 years ago. But thanks for the info I will go back and compare the reading and send a screen shot if possible.

Originally Posted by mcdavidhome

Ok thanks. I think when I looked at the live data I did see the upstream sensor readings fluctuate but I also think the downstream were fluctuating also but not as much as the upstream o2. Its just hard to believe that my CAT is bad again becuz it was just replaced by the dealer under warranty about 2 years ago. But thanks for the info I will go back and compare the reading and send a screen shot if possible.

Yeah, that seems to be pointing to the catalytic converter. I just think the catalytic converter in the Grand Prix is not that long lasting. For the fours years I owned my 2005 Grand Prix base model, I had two catalytic converter broken. At least a bad catalytic converter, unless it is clogged, is not going to influence how the car drives. If your state does not do emission test and you can live with a constant on check engine light, you should be able to drive the car just fine.

Originally Posted by Coldwaves

Yeah, that seems to be pointing to the catalytic converter. I just think the catalytic converter in the Grand Prix is not that long lasting. For the fours years I owned my 2005 Grand Prix base model, I had two catalytic converter broken. At least a bad catalytic converter, unless it is clogged, is not going to influence how the car drives. If your state does not do emission test and you can live with a constant on check engine light, you should be able to drive the car just fine.

Yes my state does not do emission test and I could easily cut my CAT off but I'm afraid that without the cat I would get bad gas mileage due to the O2 sensor readings being off. I have heard some people say you can do the non spark fouler trick to get the o2 sensors to show good readings to fool the Computer but I don't know how reliable that is..