Abstract: The device can be applied to vehicles provided with an electronic control device for the vehicle engine. The protecting device for includes a keyboard for entering a user's code, a microprocessor for converting entered data coming from the keyboard into an output message containing the user's code, programmable and non-volatile memory for storing the code for unlocking the engine electronic control device, a microprocessor for comparing the unlocking code stored in the memory with the user's code contained in said message coming from the keyboard and unlocking the engine electronic control device when there is coincidence of the code contained in the memory with that contained in said output message, and the microprocessor and the memory being capable of effecting replacement of the unlocking code of the engine control device with a new unlocking code through action on the keyboard.