| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To improve the accuracy of failure diagnosis which is performed in accordance with the output of an air-fuel ratio sensor. <P>SOLUTION: The air-fuel ratio sensor 28 of a limiting current type is installed in an exhaust pipe 26 of an engine 11. From a voltage variationΔV and a current variationΔI when varying voltage applied to the air-fuel ratio sensor 28 in a positive direction (or in a negative direction), an element resistance value Z (=ΔV/ΔI) is calculated as substitute information for an element temperature. Depending on whether the element resistance value Z is lower than a resistance value (60Ω, e.g.) equivalent to a lower limit temperature in a completely active temperature range or not, whether the air-fuel ratio sensor 28 is in a completely active condition or not is determined. In a period when that the air-fuel ratio sensor 28 is in the completely active condition is determined, the failure diagnosis of a fuel supply system or others is performed in accordance with the output of the air-fuel ratio sensor 28. This prevents the failure diagnosis when the air-fuel ratio sensor 28 is in a semi-active condition and improves the accuracy of the failure diagnosis. <P>COPYRIGHT: (C)2006,JPO&NCIPI</p> |
