Ford Repair: Ford Taurus - bad gas cap, ford taurus, purge solenoid

Question
I have a 2003 Ford Taurus. A year ago, I replaced the gas cap, after the warning light had turned on. 15,000 miles later, without an incident, the light came on again. Once again I replaced the gas cap, disconnected the battery, and the light was gone. However, less than 100 miles later it came on again and wont turn off. What other problems could cause the gas cap warning light to turn on?

Answer
an evap leak can from the gas tank to engine area-your fuel system is closed and at times when conditions are correct (this varies from car to car) temp/amount of fuel in tank/run time etc. the pcm will trigger an evap test which is basically a vacuum being pulled on fuel evap system and it has to hold vacuum for so long if it doesn't it registers a small or large evap leak-things that cause this are-gas cap/vapor line/purge solenoid/filler hose a shop with smoke tester should be able to find leak and it can be very small. good luck.