Patent attributes
A failure diagnosis apparatus for secondary air supplier according to the present invention determines a failure of a secondary air supplier based on pressure and pressure pulsation in a secondary air supply path. A failure diagnosis is made by determining the presence or absence of pressure pulsation in the secondary air supply path based on a determination threshold, and in the present invention the determination threshold is varied according to a pressure value in the secondary air supply path (a smoothed value or an average value of measured pressure). This permits the apparatus to make an accurate failure diagnosis, while eliminating pressure pulsations except for that due to exhaust pulsation (e.g., that due to noise of the pressure sensor and that caused by surging of an air pump).
