Popped Serpentine caught code P0420 2.4L DOHC 98

The skinny: Innocent joy ride to Computer Store leads to Serpentine Belt disappearing somewhere on the Highway! I noticed my Battery icon blazing after trying to pass someone doing 45 in a 55 with most feeling closer to 60! I pull off into a Gas Station , pop open the hood and witness NO SERPENTINE BELT. I head back home but go to a local car shop to have the problem fixed (serviced). Before leaving the car there I drop off my wife at home maybe 2 miles down the road. I notice smoke coming from the hood. I go back to the repair shop and let them do their magic replacing the serpentine belt and tensioner on this 2.4L DOHC Interference Motor from hell with 107K miles and counting on this 98 Cavy. They're done, my battery Lamp goes back to sleep, I'm happy for about 3 minutes and begin to resume my original trip and then I see this CHECK ENGINE lamp from hell take its place! Now I jet over to a local Car Parts store and get my free code scan and VOILA CODE P0420 rears its UGLY head! Out of the 4 horrible possibilites and having had some sort of aggressive oil leak that kept me more on top of periodic oil changes, I really hoping against hope that I don't have problem #1 or #4
Any professional opinions are welcome!
......from the ticker.....
" P0420
Definition: Catalyst efficiency low bank 1
Explanation: Oxygen sensors monitor Cat Converter's abaility to store Oxygen
Probaby Causes:
#1 Catalytic Converter defective (failure possibly due to #2,3, or 4)
#2 Engine Misfire or running condition
#3 Large Vacuum leak
#4 Engine Oil leakage into exhaust valve guide seals, piston rings'
if its #4, it'll be time to run fast off of a short tall building rooftop!

Lol...................Can`t help you with a professional opinon ,but your problem description is a very entertaining write up. Good Luck and ya lets hope it`s not #4

I'm not sure how these two problems could be related, maybe low voltage from the belt being off?? when they read the codes did they reset the cel? if so, did it return a second time?

I wish it was a low battery condition. The Battery was fine so I doubt that caused the code to pop up. My guess is since I have had an aggressive oil leak that probably stemmed from a loose timing chain gasket from when I had my water pump replaced, got worse and worse. I had my brakes done just two weeks previous and noticed the leak near those rubber boots they have on the steering and suspension stuff. So long as it's outside the engine and I'm not talking about a valve job, (I think I can safely dismiss a cracked block) I'll have to save up enough loot to have the engine dismantled from the exhaust manifold and get that gasket replaced along with any other ones. This car has been spraying oil for quite some time, I'm thinking that the O2 sensors just gave up and collectively said, "You've got to be kidding if you think I'm going to continue to look the other way with this oily Oxygen you've got circulating near your Catalytic Converter.

The 2.4 L is a real bear to work on. You could try to re -torque a few bolts on this motor to help with oil leaks. But you should be careful as this motor is alum. you could strip bolts out if you do not follow torque spec's. the cover (IDI)for the spark plugs contains the bolts that hold the cams in place which are located over the head . The cam towers are what is probly leaking and re-torque could help. Cam covers can not be removed unless you remove all the timming gears and chain. the 30.00 dollars charged for the cover gaskets is most resonable but the work and other gaskets required to get there for the cam cover gasket replacement is a challange .So take pen and paper to auto store and write down you torque application for your year and retorque see page 2b2 in haynes manual for specs and year
If your car does run good and has no missing going on and your injectors are not putting excessive fuel to exhaust then you can probly rule out #1 as high fuel to cat will cause damage to cat. also you can run car at say 2,00o RPMS till warmed up good and check cat .to see if it turns red (look under car) or have you smelled the cat of dead stench from the cat already burned but did not know.The damn o2 could also be fried even though it has not thrown code could be reading wrong if this car is 96 model and above 2- O2 sensors the heated one in the back after cat ????? NOt a mentioned as part of possible promlems but it is in the GM service Manual to check it
A very good spot to check for vaccum leaks is at the map sensor under black intake at TB this is Major problem on these cars Good luck let us know

Thanks for that feedback. I'm beginning to think that the O2 sensor(s) went blind for whatever reason and told the ECM "I've got Nothin' ". So maybe the computer can't regulate the EGR stuff. What causes it to go blind all of a sudden? Maybe engine trauma from not having a Serpentine at highway speed for a while. The torquing suggestion is worth trying with the proper tools which I don't have but perhaps can rent or something to that effect. I say I still lose a quart every 4 to 6 weeks which still isn't that bad; not quite an oil fountain as yet.