check engine light comes on

I have a 1998 Ford Explorer. The check engine light came on. I had it checked, I was told it was the gas cap, I bought a new one. After a week the light will come back on. I can drive it awhile and it will go back off. I had it checked again, I was told it was emissions. I have had the exhaust checked it is ok. I had it tested again, they still say it has something to do with the gas cap. Still confused! Can someone please tell me what I might need to get checked to solve this problem. THANKS!!

You probably got an evaporative leak code. When the gas cap fails to fix it the next probable thing is the vent solenoid for the charcoal canisters. This solenoid is located above the spare tire and is about $36 from dealer. It is in a location that gets water spray that can cause it to rust and bind open. The low tech method is if it looks bad, it probably is. Valve is normally open with power removed so you would have to apply power to see if it closes.