Diagnosis device and diagnosis method for turbocharger

A diagnosis device for a turbocharger, the turbocharger mounted on an engine, the turbocharger including a turbine, and the turbocharger being configured to supercharge intake air by driving the turbine with a flow force of exhaust gas of the engine, the diagnosis device comprising

• an electronic control unit configured to:
• calculate a turbine expansion ratio as a ratio of a pressure of the exhaust gas flowing into the turbine to the pressure of the exhaust gas flowing out from the turbine;
• operate a deterioration evaluation value toward a predetermined one of an increase side and a decrease side when the turbine expansion ratio exceeds a threshold;
• and
• determine a replacement timing of a turbine component when a total operation amount of the deterioration evaluation is equal to or larger than a specified value, the total operation amount being an operation amount from an initial value of the deterioration evaluation value.