Engine light Flashes

I was wondering if anyone has come across this. I have a 96 z71 when I start the truck and let it run for a couple of mins. The engine will turn on and then flashes. I drive half way down the street and the light turns off. Only does it when the truck has sat for a fews hours basucally when it is cold. Any ideas or suggestions? the truck runs great thanks.

Your need to have your computer scanned for codes.

Oh yea I forgot to mention that I have scanned the truck for codes and nothing comes tried 2 diiferent types of scanners and nothing.