Vehicle bypass catalyst diagnostic system

An internal combustion engine system comprising:

• an internal combustion engine;
• a main exhaust aftertreatment system with a main catalytic converter configured to receive exhaust gas from the internal combustion engine;
• a light-off catalyst bypass system with a bypass passage and a bypass catalytic converter configured to selectively receive exhaust gas from the internal combustion engine;
• an exhaust manifold configured to supply exhaust gas through a main outlet duct to the main exhaust aftertreatment system and the main catalytic converter, wherein the bypass passage is in fluid communication with the exhaust manifold;
• a bypass valve configured to move between a first position that enables exhaust gas to flow through the bypass passage, and a second position that prevents exhaust gas flow through the bypass passage and bypass catalytic converter;
• a turbocharger having a turbine, wherein the bypass passage is configured to bypass the turbine;
• and
• an emissions control system including a controller in signal communication with an oxygen sensor disposed downstream of the bypass catalytic converter, wherein the emissions control system is configured to perform a diagnostic of the bypass catalytic converter, comprising:
• monitoring, by the controller, signals from the downstream oxygen sensor for a predetermined time period during an engine cold start condition;
• determining, by the controller, a curve plotting oxygen content at the downstream oxygen sensor over the predetermined time period, based on the signals from the downstream oxygen sensor;
• determining, by the controller, a number of times the curve crosses a predetermined setpoint over the predetermined time period;
• and
• comparing, by the controller, the number to a predetermined threshold to determine if the bypass catalytic converter has failed,
• wherein when the bypass valve is in the first position, the turbine is operated in a reverse rotation to facilitate preventing the exhaust gas from passing through the turbine.

A diagnostic method for a bypass catalytic converter of an internal combustion engine system comprising:

• an internal combustion engine;
• a main exhaust aftertreatment system with a main catalytic converter configured to receive exhaust gas from the internal combustion engine;
• a light-off catalyst bypass system with a bypass passage and the bypass catalytic converter configured to selectively receive exhaust gas from the internal combustion engine;
• and
• an emissions control system including a controller in signal communication with an oxygen sensor disposed downstream of the bypass catalytic converter, the diagnostic method comprising:
• detecting, by the controller, an engine cold start condition;
• performing, by the controller, a fuel rate cycling to fluctuate an engine fuel control between lambda rich and lambda lean;
• monitoring, by the controller, signals from the downstream oxygen sensor for a predetermined time period during the fuel rate cycling and engine cold start condition;
• determining, by the controller, a curve plotting oxygen content at the downstream oxygen sensor over the predetermined time period, based on the signals from the downstream oxygen sensor;
• determining, by the controller, a number of times the curve crosses a predetermined setpoint over the predetermined time period;
• and
• comparing, by the controller, the number to a predetermined threshold to determine if the bypass catalytic converter has failed.