My check engine light comes on and off. The car runs fine.

What is your question?

When I go to my local Auto Zone, they put the hand held diagnostic device on the car and it says, "check emissions, fuel system. I have that "no gas cap" fuel filler pipe. Is there a fix for this problem? Having the check engine light go on and off is really a pain in the ass. The car has over 85,000 miles on it and it runs great!! It seems to be temperature related. Now that the warmer weather is here, the check engine light has come back on. They reset it at Auto Zone, but it comes back on a few days later. Is this a common problem with Mariners? Thanks for your help!!