| 摘要 |
PURPOSE:To make it possible to detect accurately the wire of a heater by a method wherein a bias voltage impressed upon a grounded electrode which is one of a pair of electrodes of an O2 sensor provided with the heater capable of heating an oxygen ion conductive solid electrolyte is compared with a reference value. CONSTITUTION:An O2 sensor 10 is formed of a sensor section 11 having the pair of electrodes on both surfaces, respectively, of the oxygen ion conductive solid electrolyte and a heater 2. The sensor section 11 is connected to an air-fuel ratio control circuit 15 through a terminal S and the heater 2 is connected to a power source 14 through a terminal H. In this case, a diode 13 adopted to impress a positive bias voltage of higher than a predetermined value upon one of the electrodes of the sensor section 11 and a resistor 16 is connected parallel to the diode 13. Then the bias voltage generating due to the parallel connection is inputted to a capacitor 17 and is compared to the reference voltage. Thus, when the bias voltage is lower than the reference voltage, it is judged that the wire of the heater 2 is broken and the control of the air-fuel ratio is switched from a feedback control to an open control. |
