2005 Buick Rendezvous gas cap

Hi:
Are you getting an EVAP code when the light comes on? You may need a new gas cap, or there may be a leak in the EVAP system. What I suggest is to take the vehicle to a shop and have them "Fog" the EVAP system. What they do is place a fog in the system so they can identify where the leak is located. If you don't do this, it's very hard to find the problem.

Let me know if you have other questions.

Joe