Error detection test device (15; 25; 35) for a subscriber station (10; 20; 30) of a serial bus system , having an evaluation module for evaluating which bit in a signal (TXD; RXD) must be disrupted so that the receivers of the resulting signal (TXD; RXD), in which the at least one bit is disrupted, can test the function of a predetermined error detection mechanism, wherein the signal (TXD; RXD) is processed, during operation of the subscriber station (10; 20; 30), by a protocol control unit of a communication control device of the subscriber station (10; 20; 30) in order to be transmitted as a frame onto a bus of the bus system or, after a frame has been received from the bus , to decode the signal (RXD) from the frame , and at least one input connection (1521; 1522) for receiving information relating to the signal (TXD; RXD) from the protocol control unit , at least one counter for counting bits of the signal (TXD; RXD), at least one configuration register for specifying a predetermined counter value for the counter after the error detection test device (15; 25; 35) has been switched on, and at least one output connection for outputting a switching signal (S_INV) to the communication control device in order to disrupt the at least one bit evaluated by the evaluation module in relation to the signal (TXD; RXD) output by the protocol control unit , wherein the at least one counter is configured to count each bit of the signal (TXD; RXD) on the basis of the information received at the at least one input connection , and wherein the evaluation module is configured to generate the switching signal (S_INV) on the basis of the at least one bit evaluated by the evaluation module if the at least one counter assumes the value of one of the configuration registers . an evaluation module for evaluating which bit in a signal (TXD; RXD) must be disrupted so that the receivers of the resulting signal (TXD; RXD), in which the at least one bit is disrupted, can test the function of a predetermined error detection mechanism, wherein the signal (TXD; RXD) is processed, during operation of the subscriber station (10; 20; 30), by a protocol control unit of a communication control device of the subscriber station (10; 20; 30) in order to be transmitted as a frame onto a bus of the bus system or, after a frame has been received from the bus , to decode the signal (RXD) from the frame , and at least one input connection (1521; 1522) for receiving information relating to the signal (TXD; RXD) from the protocol control unit , at least one counter for counting bits of the signal (TXD; RXD), at least one configuration register for specifying a predetermined counter value for the counter after the error detection test device (15; 25; 35) has been switched on, and at least one output connection for outputting a switching signal (S_INV) to the communication control device in order to disrupt the at least one bit evaluated by the evaluation module in relation to the signal (TXD; RXD) output by the protocol control unit , wherein the at least one counter is configured to count each bit of the signal (TXD; RXD) on the basis of the information received at the at least one input connection , and wherein the evaluation module is configured to generate the switching signal (S_INV) on the basis of the at least one bit evaluated by the evaluation module if the at least one counter assumes the value of one of the configuration registers . <EOS>