A diagnostic device for a switching device having a switching module, the switching module having an input, an output, a switching member and a trigger system, characterised in that the switching member being configured to switch between a first position in which the switching member electrically connects the input and the output and a second position in which the switching member electrically isolates the input from the output, the trigger system being suitable for controlling switching of the switching member from the first position to the second position, the trigger system being a magneto-thermal trigger system configured to control switching when one of a first criterion or a second criterion is verified, the first criterion being the fact that a first temperature of an element of the trigger system is greater than or equal to a temperature threshold, the second criterion being the fact that a magnetic field is greater than or equal to a field threshold, the magnetic field being generated by an electric current flowing between the input and the output when the switching member is in the first position, the diagnostic device comprising a controller configured to detect switching of the switching member from the first position to the second position, the diagnostic device comprising a temperature sensor configured to estimate values of a second temperature of the switching device, and a current sensor configured to measure values of a current intensity of the current, the diagnostic device being characterised in that the controller is configured to, following the detection of a switch, diagnose the switching as being a switching due to the first criterion when at least one current value is greater than or equal to a said third current threshold, the third current threshold being a function of at least one of the estimated second temperature value(s). the diagnostic device comprising a controller configured to detect switching of the switching member from the first position to the second position, the diagnostic device comprising a temperature sensor configured to estimate values of a second temperature of the switching device, and a current sensor configured to measure values of a current intensity of the current, the diagnostic device being characterised in that the controller is configured to, following the detection of a switch, diagnose the switching as being a switching due to the first criterion when at least one current value is greater than or equal to a said third current threshold, the third current threshold being a function of at least one of the estimated second temperature value(s). a temperature sensor configured to estimate values of a second temperature of the switching device, and a current sensor configured to measure values of a current intensity of the current, the diagnostic device being characterised in that the controller is configured to, following the detection of a switch, diagnose the switching as being a switching due to the first criterion when at least one current value is greater than or equal to a said third current threshold, the third current threshold being a function of at least one of the estimated second temperature value(s).