Abstract: An internal combustion engine system includes an internal combustion engine, a main exhaust aftertreatment system with a main catalytic converter configured to receive exhaust gas from the internal combustion engine, and a turbocharger turbine selectively rotatable in a first direction for a normal operation and an opposite second direction for a reverse rotation operation. A light-off catalyst bypass system with a bypass passage and a bypass catalytic converter is configured to selectively receive exhaust gas from the internal combustion engine and bypass the turbine. During cold start, long idle, and/or low main catalytic converter temperature conditions, the turbine is rotated in the second direction to restrict or prevent exhaust gas from flowing through the turbine to facilitate directing the exhaust gas through the bypass passage and the bypass catalytic converter.