The radio/cassette recorder/CD player unit fitted as standard equipment by BMW has a special code to prevent theft. Disconnecting this unit from the power supply activates the theft prevention system.
Even if power is restored to the unit immediately after the shutdown, it will not work until then. until the appropriate code is entered. Therefore, if you do not know such a code, do not disconnect the negative battery cable and do not take the unit out of the car.
The procedure for reprogramming the unit after disconnecting the supply voltage from it depends on the model. Detailed information about this can be obtained from the manual supplied with the unit or from BMW dealers