Patent ID: 8573042

Claim:
A method for use in air fuel ratio measurement, comprising: measuring an output characteristic of an air fuel ratio detecting module that is provided to an exhaust gas collecting part of an engine and outputs a value related to an oxygen concentration in an exhaust gas flowing in the exhaust gas collecting part, the measuring being based on an output value of the air fuel ratio detecting module at a time of changing a fuel injection amount, wherein the changing of the fuel injection amount during which the measuring of the output characteristic occurs is accomplished by: performing at least one of the following under a predetermined condition: starting an increase in the fuel injection amount at a particular cylinder, and continuing the increase in the fuel injection amount for a given time period; and starting a decrease in the fuel injection amount at the particular cylinder, and continuing the decrease in the fuel injection amount for the given time period; calculating a correction value for correcting the output value of the air fuel ratio detecting module based on the output characteristic of the air fuel ratio detecting module; correcting the output value of the air fuel ratio detecting module based on the correction value; and detecting a cylinder-to-cylinder gap abnormality of an air fuel ratio of supplied air fuel mixture based on the corrected output value of the air fuel ratio detecting module.