A method for controlling an exhaust system for an internal combustion engine of a vehicle includes flowing exhaust gas to a main catalytic converter (4) provided in a main passage (3), flowing exhaust gas to a bypass catalytic converter (8) provided in a bypass passage (7), detecting a predetermined condition related to a poisoning amount of the bypass catalytic converter, and blocking the main passage at least partially in response to the satisfaction of the predetermined condition, thereby causing more of the exhaust gas to flow to the bypass passage.