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​While sitting at a light, my irritating ses light came on, now what! I ran the codes and p0420 came up. After researching the code it came to the catalytic converter, fuel mixtures and air out of whack. I have noticed lately I've been burning an awful lot of fuel, however, my indicator says I'm getting 17.3 in the city, but my pocket says different. All 3 O2 sensors are new oem brand and no codes exist for such fault in my system. I did noticed that the air pump in the front on the left behind the bumper seems to be falling apart (Brittle) may need to be changed. Could this be a concern that could cause this code? I seem to have a funky exhaust smell from time to time and maybe that's a warning sign that lead to this code. Any help would be appreciated! :wipetears

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When the car is open loop, the secondary air injection pump supplies the cat with a burst of fresh air that lites up the cat. If the downstream (after cat) o2 sensor does not detect a change in the downstrean o2 sensor waveform when the air pump is running, it trips a trouble code. I have heard of some different variations of the p0420 coming on even in closed loop due to a faulty air pump.

Unfortunately, a partially plugged up cat can cause a p0420, and it can also force exhaust gases back thru the second air injection plumbing if there is enough pressure - and that can be the funky exhaust smell. It can also start melting it as well.

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If you installed Bosch O2 sensors...and now you have the catalyst code...my money is on the Bosch O2 sensors causing the false code.

I have seen this exact problem before. Same code.

Others too.....

http://www.pontiacbonnevilleclub.com/forum/2000-2005-other-than-gxp/topic2544.html

The Bosch simply work different enough...where it causes false catayst codes on GM.

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If you installed Bosch O2 sensors...and now you have the catalyst code...my money is on the Bosch O2 sensors causing the false code.

I have seen this exact problem before. Same code.

Others too.....

http://www.pontiacbonnevilleclub.com/forum/2000-2005-other-than-gxp/topic2544.html

The Bosch simply work different enough...where it causes false catayst codes on GM.

I think the secondary air injection pump needs replacing, however, I will be replacing all Bosch 02 sensors this week. I've been running premium fuel for a while, any harm in doing this?

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