METHOD FOR DIAGNOSING UNUSUAL CONDITIONS OF GAS CONCENTRATION DETECTING UNIT, AND APPARATUS FOR DIAGNOSING UNUSUAL CONDITIONS OF GAS CONCENTRATION DETECTING UNIT

摘要

Unusual condition diagnosing method and apparatus capable of determining, with reliability, an abnormal condition when it occurs in a common wiring connecting a gas sensor with a control circuit that drives and controls the gas sensor. A gas concentration determining unit (1), which is connected to a sensor element (10) including an oxygen pump cell (14) and an oxygen concentration detecting cell (24), has a sensor control circuit (50) for driving and controlling the sensor element (10). In the concentration determining unit (1), an abnormal condition detecting circuit (53) and an arithmetic operation part (54) are used to detect a variation of a terminal voltage at a connection node (specifically, Vs+ terminal) except a connection node between a common wiring (42) and each of the electrodes facing to the determination chambers of the cells (14,24). A diagnosis of an unusual condition of the common wiring (42) is performed based on the variation of that terminal voltage. If the common wiring (42) is broken, the terminal voltage at the Vs+ terminal exhibits a voltage variation accompanying an oscillation. Then, the abnormal condition detecting circuit (53) and arithmetic operation part (54) detect this voltage variation accompanying the oscillation, thereby providing an abnormal condition determining signal to a CPU.