Deteriorated condition detecting apparatus for an oxygen sensor

摘要

An apparatus for detecting a deteriorated condition of an oxygen concentration sensor mounted in an exhaust pipe for an internal combustion engine for controlling an air-fuel ratio is described. The apparatus includes, in addition to the sensor, a reference oxygen concentration sensor mounted in the exhaust pipe downstream of a cleaning device, and a discrimination unit for determining the deterioration of the oxygen concentration sensor for controlling the air-fuel ratio by measuring at least one of a duty factor and a period of an output signal from the reference oxygen concentration sensor.