Heater control device for an air-fuel ratio sensor

Claim 1

A heater control device for an air-fuel ratio sensor which comprises: an air-fuel ratio sensor comprising a sensor element which detects an air-fuel ratio state of exhaust gas of an engine, and a heater which heats the sensor elements; a heater current flow control means for controlling current flow through the heater to maintain a predetermined constant temperature; a harness having a plurality of couplers at both ends thereof which connects between the air-fuel ratio sensor and the heater current flow control means via connection lines, wherein said harness and said heater current flow control means are arranged such that a resistance value of said connection lines is negligible with respect to a resistance value of the heater, and wherein a total resistance of said plurality of couplers, said connection lines and the heater is substantially equivalent to said resistance value of the heater; and a current detecting resistance which is connected to the heater in series and detects current of the heater, wherein said current detecting resistance is arranged in one of two locations including a first location adjacent to said coupler on the air-fuel ratio sensor side and a second location being incorporated in the coupler on the air-fuel ratio sensor side.