Now what do I do? Dreaded P0420

[djclac]

Brief History:2006 Vibe 2wd. One of the early PCM replacements put in the car prior to the recall. I get the code for teh Evap System once in a while if the wife doesnt put the cap on tight...P0420 showed up and I started looking...Found lots of great answers and since the car is now paid for, decided to do the full monty on the exhaust system to take care of the problem.I bought the Cat Assembly from a web site that offered it for $300 delivered, Got two new O2 sensors Upstream --Nippondenso Downstream Bosch both from Advanced Auto--about $250 total. And replaced the plugs (Denso plugs about $9 each) for good measure. Car has about 85k on the clock.Well that cleared the code for about 55 miles or so. I cleared the code again and the wife said the light came backj on the next day after returning from work.Anyone know what the o2 sensor voltages are supposed to be? The Scan tool I have tells me what the voltages are, I have to assume that this is the problem the rear one is getting more voltage than it should.The upstream is about 3.2v at idle and the downstream is about .990 to 1.0vso just short of replaceing everything again (this time with all Factory parts) any ideas?

[DiveNut]

Hi djclac,Check for exhaust leaks at the exaust manifold, Flange, CAT etc. Some claim a leaking intake manifold can cause the 0420 as well.Pat