Diagnosis device for internal combustion engine, and diagnosis method for internal combustion engine

A diagnosis method for an internal combustion engine that is mounted on a vehicle, the internal combustion engine including an EGR device, an air flow meter and an electronic control unit, the diagnosis method comprising:

• executing, by the electronic control unit, EGR diagnosis processing to diagnose whether or not the EGR device operates normally while the vehicle is decelerated;
• executing, by the electronic control unit, air flow meter diagnosis processing to diagnose whether or not the air flow meter is normal while the vehicle is decelerated;
• diagnosing, by the electronic control unit, the EGR device as normal in the EGR diagnosis processing when a differential pressure between a first intake pressure and a second intake pressure is equal to or higher than an abnormality determination value, the first intake pressure being an intake pressure in an intake pipe of the internal combustion engine that is determined when an EGR valve of the EGR device is closed, and the second intake pressure being an intake pressure in the intake pipe that is determined when the EGR valve is open;
• executing, by the electronic control unit, the EGR diagnosis processing after starting the air flow meter diagnosis processing;
• and
• executing, by the electronic control unit, the EGR diagnosis processing when the air flow meter diagnosis processing has not been completed and a predetermined condition that a duration of deceleration of the vehicle is shorter than a diagnosis time that is required to execute the air flow meter diagnosis processing are fulfilled.