P0303 should be a cylinder misfire code, pertaining to cylinder 3, its not affecting at ignition, but it picked up either an electrical or mechanical misfire. You may also want to ensure your fuel injectors are not clogged with fuel debris.
do not always assume its electronic ignition problem... you can have a faulty injector, cylinder is not reaching to its full potential during combustion stroke, or wrong grade of fuel. Cannot tell you what the "actual" problem is without diagnosis of electrical equipment. So never assume that its always a electronic failure. some people on here will tell you what they "think" it is for common failure, but your best option is to take it down to a dealership with people who "know" what to diagnosis with rather than a google assumption and paying bucks out of your pocket for not the cause of your engine code.
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 Coby7; 10-03-2013 at 04:26 PM.