A method for operating a data processing unit of a driver assistance system, the unit including main and slave computers. The main computer ascertains surroundings data from a surroundings detection system by using a processing specification. The slave computer operates a communication interface of the data processing unit, using a communication instruction. The method includes initializing, a first testing, a carrying out, a second testing and a forwarding. In initializing, the main computer, in response to a signal, is initialized by performing an initialization instruction on the main computer. In the first testing, the slave computer, in response to the signal, is initialized by performing a self-test instruction on the slave computer. In the carrying out, the communication instruction is performed on the slave computer to send and/or receive data via the communication interface, when the slave computer is tested and while the main computer is initialized. In the second testing, the main computer is tested by performing a test instruction on the slave computer, when the main computer is initialized. In the forwarding, the surroundings data are forwarded via the communication interface by performing the communication instruction on the slave computer, when the main computer is tested.