A device for a vehicle including: a memory configured to store mapping data including machine learning data defining a mapping that uses an estimation variable that is a variable indicating a vehicle operation status of the vehicle and a detection value of a sensor detecting an oil temperature of a power transmission device as input variables, and uses an element corresponding to the input variables as an output variable; and a processor configured to: acquire the input variables; use the mapping to acquire the element as the output variable of the mapping corresponding to the input variables; and determine based on the element whether the detection value becomes equal to or higher than a threshold value due to occurrence of an abnormality in the power transmission device or a mode of vehicle operation by the driver of the vehicle.