Method and system for controlling air/fuel level for internal combustion engine with two exhaust banks

A method and system for controlling the air/fuel ratio in an internal combustion engine (12) having first and second groups of cylinders coupled to first and second exhaust banks, respectively. The first exhaust bank includes a catalyst (20) and at least a pre-catalyst oxygen sensor (18). The second exhaust bank includes a catalyst (24) and no more than one post-catalyst oxygen sensor (26). The oxygen sensors monitor the oxygen content of the exhaust gases in their corresponding exhaust banks and provide feedback signals to a controller (202). The controller (202) uses the feedback signal from the pre-catalyst oxygen sensor (18) to calculate desired A/F values in the first group of cylinders. The controller uses both the feedback signal from the pre-catalyst oxygen sensor (18) and the feedback signal from the post-catalyst oxygen sensor (23) to calculate desired A/F values for the second group of cylinders.