Patent ID: 7140177

Claim:
A secondary air supply system that supplies secondary air to each of exhaust pipes attached to each of two banks of an internal combustion engine via a secondary air supply pipe including a joint portion and two branch portions divided from the joint portion, the secondary air supply system comprising two air control valves respectively provided in the two branch portions, and a pressure sensor provided in the joint portion of the secondary air supply pipe, wherein an abnormality diagnosis is executed with respect to the two air control valves which are opened at different timings, the two air control valves including a first air control valve that is firstly opened and a second air control valve that is secondly opened, based on a combination of a fluctuation of a pressure in the joint portion detected by the pressure sensor upon opening of the first air control valves and a fluctuation of a pressure in the joint portion detected by the pressure sensor upon opening of the second air control valve.