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 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 (1521, 1522), 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 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 (1521, 1522), 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.