Detection of malfunction in gas concentration detection system

摘要

A gas concentration sensor voltage and current (in both heater on and heater off states) are detected and compared with predetermined thresholds, respectively, by a microcomputer. Based on a combination of the comparison results, the presence or absence of trouble in the system is detected and trouble location in the system is specified. In addition or alternatively, the sensor voltage is compared with thresholds to determine whether it is outside of a normal zone. The voltage may be actually detected or calculated. If the voltage is outside the normal zone, sensor voltage is reduced to zero or restricted to a predetermined limit.