GM reports that the cruise control systems on some 2005-10 Chevy Cobalt and 2007-10 Pontiac G5 models may not function properly. One possible cause is that the cruise option was not enabled or the option was defaulted off after checking to see what options were enabled by the BCM during a previous repair.
A quick check is to hook up a scanner and confirm that the cruise option is turned on in the BCM. If it isn't, select cruise, save, then exit out and verify that the cruise control system is functional. If the cruise system is enabled or enabling it doesn't get the system working then this information doesn't apply; continue with conventional diagnosis until the problem is resolved.