On vacation in Florida, 1200 miles from home. Check engine light illuminates and I was lucky enough to be in an area where there was a dealer who stayed open later in the evening. The gentleman at the entry gate ran the code and it came back as a gas cap failure. Purchased and installed new cap and dealer reset computer. This seemed to be a cheap and easy fix. Approximately 800 miles into my return trip I recieved the same code via On-Star. I have replaced the cap 3 times with OEM equipment. Problem still exists. No problems with performance but I live in an area that requires emission inspections and now the code returns before the 100 mile requirement for the state regualated equipment will allow my inspection.