2007 Chevy Cobalt CEL but No codes

Sometimes your check engine light will flash, but your computer won't retain the code if it doesn't reoccur often enough. But if your light stays lit, then the computer should definitely have a code waiting for you.

When you had it scanned, what kind of scanner did you/they use? All scanners aren't created equal.

If you haven't already done so, have your computer scanned by a GM code reader that will have the capability to monitor all of the systems in real time as you drive.

If you can't interpret the information, have a mechanic do it.

This will pinpoint your problem without you having to chase down ghosts. That would only waste your time and money.