Memory disabling device for engines fed with one or other of two fuels

A device for engine-driven vehicles provided with a battery and feedable with one or other of two fuels, namely a primary fuel (for example petrol) and a secondary fuel (for example gas) via a changeover switch, and comprising a central electronic engine control unit (4) with which a diagnostic memory (5) is associated to memorize operating errors on switching-off the engine, in which on switching-off the engine when fed with the secondary fuel (for example gas) the diagnostic memory (5) is disabled by interrupting its electrical connection to an electrical power source.