Method and system for diagnosing undeactivated valve of deactivated engine cylinder

The present disclosure provides methods and systems for diagnosing an undeactivated valve of a deactivated engine cylinder. Methods and systems are provided for a diagnostic procedure for a variable displacement engine (VDE) of a vehicle to detect an undeactivated valve of a deactivated cylinder due to a degraded valve deactivation mechanism. In one example, a method includes, during operation of the VDE with one or more cylinders of the VDE deactivated, calculating changes in rapidly sampled signals output by one or more exhaust oxygen (EGO) sensors of the VDE during a plurality of engine cycles; determining that the change is greater than a threshold change; and in response, indicating that valves of the one or more cylinders are not deactivated. A second method includes estimating a throttle airflow rate and an engine airflow rate of the VDE; and indicating an undeactivated valve of one or more deactivated cylinders if the throttle airflow rate exceeds the engine airflow rate by a certain threshold. 本公开提供了