A control apparatus performs a diagnosis process for determining whether or not catalyst warm-up control is abnormal by determining whether or not an ignition timing that is set during the performance of catalyst warm-up control is a timing advanced by a threshold or more. The threshold is a value that is set to a timing more advanced than the ignition timing that is set during the performance of catalyst warm-up control by a predetermined margin. The control apparatus performs a setting process for setting the threshold based on a start-up coolant temperature such that the margin becomes larger when the start-up coolant temperature is low than when the start-up coolant temperature is high.