Vehicle bypass catalyst diagnostic system

Abstract

An engine system includes an internal combustion engine, a main exhaust aftertreatment system with a main catalytic converter, and a light-off catalyst bypass system with a bypass passage and a bypass catalytic converter. An emissions control system includes a controller in signal communication with a first temperature sensor disposed upstream of the bypass catalytic converter, and a second temperature sensor disposed downstream of the bypass catalytic converter. The emissions control system performs a diagnostic of the bypass catalytic converter, including (i) monitoring signals from the first and second temperature sensors for a predetermined time period during an engine cold start condition, (ii) determining a temperature of an inlet of the bypass catalytic converter, (iii) determining a temperature of an outlet of the bypass catalytic converter, and (iv) comparing the bypass catalytic converter outlet temperature to the bypass catalytic converter inlet temperature to determine if the bypass catalytic converter has failed.