I am not sure what the problem might be if you left the gas cap off but if he reset it once thats okay but if it came on again i would have it checked if it was related to the gas cap then the computer allowed the reset and if it came up again (and if its related to the gas cap) then most likely theres a real problem, and if its not related to the cap then you will be glad that you checked it out and if money or hassle drives you nuts at the dealerships check around to see if you can find a diagnostic reader from someone where you live or borrow one from an autozone or pepboys usually they lend it out for a deposit.:thumbup: