Pontiac Repair: PO 420 Error Code, 2004 pontiac vibe, toyota corola

Question
Hi, I own a 2004 Pontiac Vibe and the check engine light came on. I took it to Advance Auto Parts and the diagnostics showed the above error code. I have replaced the catalytic converter and both O2 sensors and the light goes off but then comes back on after a few miles. Could there be another problem besides the two I've mentioned?  If so, what?

Answer
Hi Ricky:

did you replace the Cat converter with an original equipment converter or a fits all? That can be part of the issue. Same with the O2 sensors. that car has multiple O2 sensors that fit it depending the the emission system on the engine. Again a fits all is not "fits all" aftermarket parts cause more issues then they fix especially on foreign cars like these. this is the same car as a Toyota Corola Matrix. I would start over again with the right parts for the car not parts from Auto zone or a parts store like that. If you did use OEM parts then your going to have to have the car put on a scanner and see what the O2 sensors are doing on this car. A code reader will not do the trick you actaully need a true scan tool. good luck :)