2006 Chevy Cobalt display error code

Computer problem
2006 Chevy Cobalt Automatic 42000 miles

I used to drive a Plymouth Neon, and to display the trouble code, all you had to do was quickly within 5 seconds, switch the ignition 3 times and then back on to show any stored codes. My question is: is there a simular way with the Chevy Cobolt? I would just like to know in advance of returning my car to CarMax what codes/trouble the computer has stored. I would also like to add that while the "check engine light" came on, I cycled thru my various displays and my engine temp reading was ___ just 3 dashes, no temp reading. I pulled over after a couple of miles and my overflow fluids were not overheating. My temp readings have since returned, and are in normal ranges, but the check engine light is still lit. Thank you for any assistance, bob