2002 Oldsmobile Silhouette Gauges turn off and on among oth

Sorry I did not see you had replied to this thread. The o2 sensors are switching (both of them are). However it took a week before the cat test was done (Im too lazy to do it the correct way lol). As soon as the cat test was done the po420 fault came right back on. The o2 sensors were reading the same number but are constantly changing from rich to lean. Neither sensor stays in the middle (.45). The big reason I am leaning towards the cat being bad is because this van has had 2 eaten through head gaskets. First one at 30k miles (under warranty) second one 36k miles later (just outside of warranty). My problem is I didnt have the $$ to fix it at the time so I drove it till it had 95k miles total on the van (30k miles from when it started leaking). I now had the money to get it fixed however we kept driving it until the engine overheated on us. Thats when we took it right in. So for at least 30k miles the Dexcool was most likely leaking into the cat converter. The other thing is the 02 sensors seem kind of sluggish. As in they change value at most 2 times every second. So it could be all 3 items (up and down stream sensors and the cat). It will prob be another week before I can get the cat changed. Place around the corner from me quoted me $300 to change the cat and well thats only $50 more than I can buy a cat and do it myself so I would rather let them do it for $50 haha. Either way what do you think?

I can see how this "might" cause the issue but I swapped 2 relays (multiple relays are the same on this thing) and the problem didnt follow so I went onto the next thing. As merlin wrote I did find the issue with wiring running across the ac accumulator.

Hmm my downstream sensor is constantly switching just like the upstream sensor.

Ok finally got the van in (finally had a day off haha). You could hear the cat rattling. Either way they did it for $100 less than I could buy the material myself. Either way now the downstream is pretty constant and the upstream still constantly changes from low to high. Thanks for all yer help.