did you get the right 02 sensors? should be H02 (Heated 02 sensor) for Bank 1 sensor 1 on header, then H02 for Bank 2 sensor 1 (post-after cat). If it triggered right after the 02 installation, you either got the wrong ones, cheapos, or its detecting too rich or lean, which will throw a DTC code.
You may need to on the first 02 sensor on the header, add a spark plug anti fouler old trick for it to space out just enough for the proper readings.
Overall, use exactly what GM uses for 02's, never bosch or parts.something.com's.
Coby7 is dead on right for a TWC (Three Way Catalyst). It is used OEM on our vehicles, since we no longer require EGR valves, we use Variable Valve Timing or High Compression Pistons. You can thank the EPA for that one. You may have a faulty catalyst as well, being aftermarket, though I hear that no one has any issues with ZZP downpipes.
2009 Cobalt LS XFE U74
Mods: K&N Typhoon Intake, Option Cat-Back Exhaust, Cosmo Short shifter, Maxxim Ahead 17X7's, MPx shorty antenna, FE5 Strut/shocks, Tein S Techs, Moog endlinks, Moog spring seaters, ZZP shorty header, LSJ downpipe, LNF front grille
Last edited by 5t3alth; 05-25-2013 at 08:52 PM.