Non-intrusive exhaust gas sensor monitoring

A system for a vehicle, comprising:

• an engine including a fuel injection system;
• an exhaust gas sensor coupled in an exhaust system of the engine;
• and
• a controller including instructions executable to:
• for each entry into and exit out of DFSO, if an air-fuel ratio disturbance is not present prior to the entry or exit, then add a collected change in lambda over time during the entry or exit to a set of exhaust gas sensor responses;
• indicate exhaust gas sensor degradation based on a time delay and line length of each sample of the set of exhaust gas sensor responses;
• and
• adjust a fuel injection amount and/or timing based on the indicated degradation.

A method of monitoring an oxygen sensor coupled in an engine exhaust, comprising:

• collecting a set of exhaust gas sensor responses during entry into and exit out of DFSO;
• based on the set of exhaust gas sensor responses,
• indicating an asymmetric delay sensor degradation if one of an average entry or exit time delay exceeds a respective expected entry or exit delay;
• indicating an asymmetric filter sensor degradation if one of an average entry or exit line length exceeds a respective expected entry or exit line length;
• and
• adjusting a fuel injection amount based on an indicated sensor degradation, wherein the indicating includes generating an indication light.