P0420 Reoccurring, Super Annoying

[Jersey07GT]

Hey guys, my name is Christopher I have followed the forums for a quite a while but haven't posted much, I hate to post only when I have a problem haha. Well after a recent oil change (maybe overfilled or wrong filter IDK??!) I got a CEL, I hooked up my OBD II scanner I received a code P0420 Catalyst System Efficiency Below Threshold (Bank 1) I don't want to be redundant but I love my care and maintain it meticulous. I am trying to figure out how to go about this... Should I change the O2 sensor, use the spark anti-fouler method I have read about on various forums? Maybe seaform in the gas take will do the trick? I would love to able to fix this problem without buying a replacement catalytic converter. I really can't afford to replace the cats could this be due to the O2 sensor failing or another reason ? The car is basically stock besides the Flowmaster Axleback Outlaw mufflers, I am not sure if the cat is stock, but I have never received this code before in the 6000 miles I owned the car any help would be appreciated!

 

[Marble]

In my experience...When a problem occurs after I've worked on my car it's because I've screwed something up during the repair or maintenance.

I would back track your oil change and make sure you inadvertently didn't screw something up.

 

[Johnf78]

Swap your O2's, reset the code and see if the code follows the O2.

 

[Pentalab]

clear the code. IF it clears,see if it comes back asap....or a week later..or maybe never.

make sure ur REAR O2 sensor cable is plugged in on that side. Bank 1 should be pass side sensor. U may have bumped something while doing the oil change.