2005 Check Engine Light

I have two lights on my dashboard, first is showing roadster top not fastened (it is) and second is the check engine light. I have tried both Audi and two different service locations and no one can scan this TT. I have checked all fluids and gas cap but have located nothing. This happened once before and the only way to get rid of the light I believe was to touch the positive and negative battery cables together to reset computer. Any advice would be appreciated. TIA