Apparatus and method for anti-theft device of a motor vehicle

In the apparatus in the control unit, a controllable switch is built in, which releases the start authorization and by means of which, can be switched off the supply voltage that is supplied to the controllable switch. For checking a start authorization so that a diagnosis can be made, which is realized via a resistor coding with known resistance elements in the power supply line between the release means and control unit. The voltage drops across the elements of the resistance network with the corresponding target values ​​can be compared. Simply shorting of the starter motor or the ignition is thus no longer possible, as this would be recognized by the control unit due to the changing thereby voltage drops. Moreover, this can be detected also defines an error in the supply voltage or the supply lines.