To highly accurately detect a failure of an exhaust system in accordance with values detected by air/fuel ratio sensors.
An engine ECU executes a program which includes a step (S102) of detecting the amount of intake air, a step (S110) of subtracting an air/fuel ratio detected by the air/fuel ratio sensor on the upstream side from an air/fuel ratio detected by the air/fuel ratio sensor on the downstream side, a step (S112) of determining a region in a low GA area in accordance with a calculated difference between the air/fuel ratios, a step (S120) for determining a region in a low GA area, and a step (S122) of determining a failure or not of the exhaust system in a A-section in accordance with a combination of the region in the low GA area and the region in the high GA area.
Toshio Morita
Takao Matsuyama
Tadashi Muto