I have a 2003 Grand Cherokee. I have been running into problems with my "check engine" light coming on. I took it to Auto Zone and they said to tighten the gas cap, it worked and the light went off. I have done it several times over the last 2 yrs. Now my light is on and won't go off. They recommended buying a new gas cap and see if it goes off. They also said it could possibly be more serious though. Any advice for me??