US Patent 7152594 Air/fuel imbalance detection system and method

A method for detecting emissions from an internal combustion engine generally including determining a reference air/fuel mixture signal based on an engine speed and an airflow into the engine. The method includes determining an actual air/fuel mixture signal from an air/fuel mixture sensor and comparing the reference air/fuel mixture signal to the actual air/fuel mixture signal. The method also includes determining whether an air/fuel imbalance condition occurs based on the comparison and setting a service indicator based on the determination of whether the air/fuel imbalance condition occurred.