Oxygen concentration detector and method of using same

摘要

An oxygen concentration detector includes an air-fuel ratio sensor, a heater that heats the air-fuel ratio sensor, a heater controller that supplies electric power to the heater such that the air-fuel ratio sensor reaches an activation temperature, and an element temperature detector that detects a temperature of an element of the air-fuel ratio sensor. The heater controller detects a rate of decrease in the temperature of the element of the air-fuel ratio sensor based on the temperature detected by the element temperature detector, and determines that the sensor element is wetted when the detected rate of decrease is greater than a reference value. The element temperature detector can detect the sensor element temperature based on an impedance of the element. The heater controller can prevent the supply of electric power to the heater if it is determined that the sensor element is wetted. The air-fuel ratio sensor can be provided in an exhaust passage of an engine.