Device for vehicle, system and method

A device for a vehicle, the vehicle having a power transmission device and a sensor that detects an oil temperature that is a temperature of oil circulating in the power transmission device, the device comprising:

• a memory configured to store mapping data including data learned by machine learning, the 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 the sensor 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 that the cause for the detection value becoming equal to or higher than a threshold value is (i) an abnormality in the power transmission device or (ii) a mode of vehicle operation by a driver of the vehicle.