A diagnosis device determines diagnoses one of primary and secondary board temperature sensors as abnormal, in response to a condition that a state in which a primary temperature sensor value and a secondary temperature sensor value deviate from each other by a predetermined value or more continues for a predetermined duration or more; performs torque limitation to limit a torque inputted from an engine to an automatic transmission, during driving in a predetermined travel section based on a predetermined condition, after the one of the primary and secondary board temperature sensors is diagnosed as abnormal; and performs transmission shift restriction to restrict shifting of the automatic transmission along with the torque limitation, in response to a condition that the one of the primary and secondary board temperature sensors continues to be diagnosed as still abnormal after the driving in the predetermined travel section is completed.