2005 Buick Rendezvous gas cap

Try having the light reset by a nationally recognized parts store to see if it comes back on. If it does, then do the following:

Take the car to a shop and have them fog the EVAP system. Somewhere in the system is a leak. The system thinks it is the cap, but 99% of the time it isn't. The fog (in the EVAP) will leak out and be visible so you can find where the leak is. Otherwise, you will be looking for for a long time trying to find a needle in a haystack.

Let me know what you find.

Joe