| 摘要 |
PROBLEM TO BE SOLVED: To improve the diagnosing accuracy by appropriately setting the diagnose allowing condition when diagnosing a failure of an air-fuel ratio sensor provided with a sensor element including a nernst cell part and a pump cell part. SOLUTION: The alternating current voltage is applied to a nernst cell part, and the impedance Ri of the nernst cell part is measured on the basis of the current (amplitude) flowing in the nernst cell part (S1). The pump current Ip in a pump cell part is measured (S2). As a result, when the impedance Ri at the predetermined value (corresponding to the predetermined active temperature or more of the element temperature) or less is detected and the pump current Ip within the predetermined range (the A/F atmosphere is specified and except for at least the fuel cutting time) is detected, failure diagnose is allowed (S3, S4-S5).
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