PURPOSE: To make the activation of an oxygen concn. sensor without using an engine running parameter possible by discriminating the completion of the activation of the oxygen concn. sensor upon lapse of the prescribed time since electric current is supplied to a heating element.
CONSTITUTION: A heater current supply circuit 25 starts supplying the heater current to the heating element of the oxygen concn. sensor 21 according to the current supply command of an air-fuel ratio control circuit 26 and stops the supply of the current according to a current supply stop command. A 1 is set at the flag for discriminating the current supply in a circuit 26 when the current supply command is generated. A 0 is set at the flag by the stop command and therefore whether the heater current is supplied or not is discriminated from the flag content. The flag 1 is set in a counter built in the circuit 26 as well and the completion of the activation of the sensor 21 is discriminated upon lapse of the prescribed time after the supply of the heater current is started. The discrimination of the activation of the sensor 21 is thus made possible regardless of the output level of the sensor 21.
KAWANABE TOMOHIKO
MATSUMOTO YORIHIRO
HASEBE HIROSHI
