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Old 04-19-2009, 01:50 AM   #11
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Originally Posted by 01bse View Post
I have a code po420 on my 01 bonneville,check eng light came on,seems to be low on power but not running rough,anyone else have this and can lead me to the problem thanks ahead
Yes i did, ended up being a bad cat. Had to take it to the dealership and have it replaced. Since it was under warranty they replaced the whole exhaust system !
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Old 04-19-2009, 02:03 AM   #12
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ok... if you have acces to an o scope, check both sensors on the bank 1 side. if they are switching at the same time, you have a bad cat. but from the sound of it, it sounds to me like you either have a lazy 02 sensor or a bad cat. Lazy 02 meaning it is not switching as many time as it should in 1 second.

On a scanner, go to live stream data list and you might be able to trell if they are switching at the same time.

The o scope is the best way to go.
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Old 04-19-2009, 02:09 AM   #13
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With the lack of power it is most likely the converter. Unbolt the front of the converter so you have open exhaust and test drive to see if the power is restored.
You can try this too, when i was at the dealership they told me that the exhaust restriction was very high and thus a drop in power. Remember that any restriction in the exhaust is taking away from your supercharger boost effect! :( this is an easy and very cheap way to tell. Also try using the O-Scope mentioned above, this helped me determine my problem too. Good Luck!
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