Heater controller for an air-fuel ratio sensor

摘要

A heater control system for an air-fuel ratio sensor is shown to prevent the sensor from being cooled during an extended idling operation after high-load running. An oxygen concentration detecting element of an air-fuel ratio sensor is heated by a heater installed in the sensor, and its temperature is controlled to about 650 DEG C. When a radiator cooling fan functions during idling or low-speed running after high-load running, a controller detects the functioning of the fan and increases an electric power supplied to the heater. A heater resistance detector detects a resistance of the heater. A storage device stores the detected heater resistance when it is determined that a temperature of the heater is stable based on an engine operating condition. Electric power supplied to the heater is increased in accordance with the difference between the detected resistance of the heater and the stored resistance. A heater controller thus prevents the air-fuel ratio sensor from being cooled by the fan to the point that detection accuracy of the sensor would deteriorate.