An on-board component abnormal site identifying method includes executing an acquisition process, a calculation process, and a reporting process by an execution device. The acquisition process is a process for acquiring, by the execution device, values of input variables. The mapping includes, as the input variables, a foreign substance variable, and includes, as an output variable, an abnormal site variable. The calculation process is a process for calculating, by the execution device, a value of the abnormal site variable by inputting, to the mapping, the values of the input variables acquired through the acquisition process. The reporting process is a process for reporting, by the execution device, a calculation result of the calculation process by operating a reporting device.