Need help - code, P0420

[energie817]

I just installed a Hytech header and exhaust with a vibrant high flow cat from Hytech also. After a week of driving the my stock 01 itr is throwing a code, P0420. Is the new cat causing this? Anyone here have similar problem after installing a new exhaust system? Any help would be appreciated. thanks

http://www.obd-codes.com/p0420

[wego5]

Just curious, Did you install the secondary o2 sensor on the high flow cat? I only ask because I am going to have an o2 bung welded on my smsp cat.