codes P1278 & P1279

[N!smo]

alright guys this is on my 05 1.8s i recently got the code for precat failure, worse gas mileage, black oil, so i replaced my header with ebay header, exhaust shop welded a cat on midpipe before 2nd O2 and i think it took care of the code. but now a new code(s) poped up the P1278 and p1279 and after doing some research i came out empty handed....

maybe i was thinking the exhaust gasket i used sucks because i hear a whistle coming out of there. but i heard something about ecu reprogramming?

[black2.5alti]

What about replacing the o2 sensors themselves?

[N!smo]

nope didnt even bother. i figured its the precat forsure so whatever... another O2 is on the way