Non-contact exhaust gas sensor monitoring

There is provided a method of monitoring a coupled to an engine exhaust gas sensor. In one embodiment of the method, each sample of a collected during a commanded change in the air-fuel ratio of the quantity of exhaust gas sensor responses comprises displaying the exhaust gas sensor function impairment based on a time delay and a line length. In this way, the exhaust gas sensor can be monitored using robust parameters in a non-contact manner.