An error detection test device for a subscriber station of a serial bus system. The error detection test device has an evaluation module for evaluating which bit of a signal must be interrupted so that the receivers of the resulting signal in which the at least one bit is interrupted can check the function of an error detection mechanism, the signal being processed by a protocol control unit while the subscriber station is in operation in order to be able 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 an output terminal for outputting a switching signal to the protocol control unit to interrupt the at least one bit. The evaluation module generates the switching signal based on the at least one bit evaluated by the evaluation module.