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

Check this out. It will help you figure out where you need to look OBD-II Trouble Code: P0420 Catalyst System Efficiency Below Threshold (Bank 1)

420 catalyst system low efficiency

Check your rear O2 sensor

would the sensor produce low power,I was thinking a bad cat since it has loss of power also

If the sensor is going bad it will trip a code. Also, if the cat is going bad, it will trip a code.

so is it the first 02 senor before the convertor the the one after the convertor if you got this code?

How can a sensor be the first check, when that is telling the computer there isn't enough of a difference from what the front and back sensors are reading?

Did a quick search and came up with the FSM info on this code.
http://www.gearchatter.com/viewtopic...ighlight=p0420

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.

this check engine light is making me mad

Rear sensor...after the cat.