HEATER CONTROL DEVICE FOR AIR/FUEL RATIO SENSOR

摘要

PROBLEM TO BE SOLVED: To provide simple and inexpensive circuit construction permitting accurate detection of a heater breakage failure in heater failure diagnosis where a current is carried in a heater for an air/fuel ratio sensor in a duty ratio control system. SOLUTION: The failure diagnosis of the heater is performed in accordance with voltage on a current carrying circuit for the heater and the current carrying condition of the heater. Current carrying time limiting means 67 is provided for setting an upper limit for a current carrying time in a preset time for the heater or a lower limit for a non-current carrying time, thus avoiding the continuous current carrying condition of a command for the duty ratio control.