GM OBD2 has to have 50 starts without ANY errors to clear the light. Now that being said, Autozone has the tools to check and clear these lights, but they will not clear them. You have to be VERY INSISTANT with them.
I have a venture and needed the light cleared after I changed the intake manifold gaskets. I had to tell the guy, "Look, I am the ONLY person who will EVER wrench on any of my vehicles, so either you will clear this light or I will find another auto parts supplier." Even after I told him this we had to wait untill there was no one in the store and no one outside, because he was afraid that someone would see him press that horrible "CLEAR" button.