Apparatus for protecting motor vehicle against unauthorized operation

Abstract

An antitheft apparatus for a motor vehicle can allow operation of an internal combustion engine of a motor vehicle to be started notwithstanding of decision of discrepancy in an engine start enabling signal ascribable to transient error in communication between a code collating means and an engine start decision means. An identification code stored in an engine key (1) is read out upon every starting of operation of the motor vehicle to be collated with a preset identification code to thereby make decision as to whether or not both of the identification codes coincide with each other. Upon decision of coincidence, the identification code as read out is affixed with a rolling code which is updated every time the engine of the motor vehicle is operated, to thereby generate an engine start enabling signal. Means are provided for sending the engine start enabling signal and for generating the rolling code. The rolling code as generated is sent to the rolling code adding means (30b). Decision is made as to coincidence between the identification code contained in the engine start enabling signal and the preset identification code, wherein upon detection of coincidence of the identification codes, the rolling code contained in the engine start enabling signal is collated with the rolling code generated by the rolling code generating means, to thereby output the engine start enabling signal to engine starting means upon detection of coincidence between the rolling codes.