CEL check code 45 Help!
 

Guys,
I have the 00 Si. I just put on a REVHARD stage II into it, now i got this code 45 adn this is the 2nd time it poped out after the kit been installed. Can someone explain to me why? Im running stock OBDII ECU with stock internal, FMU 12:1, intake fuel pump boosting 6psi max, i weld the 2nd O2 sensor to the side of the muffler piping not inside the piping, im running straight piping. Please help me out thanks.