| 摘要 |
PROBLEM TO BE SOLVED: To detect output fixing abnormality or offset abnormality of an alcohol concentration sensor detecting alcohol concentration of fuel supplied to an internal combustion engine which can use alcohol-blended fuel. SOLUTION: When predetermined abnormality diagnosis execution conditions are satisfied, an air-fuel ratio control is switched from a feedback control to an open-loop control to change a fuel injection amount at a predetermined rate to find a theoretical air-fuel ratio according to the alcohol concentration detected by an alcohol concentration sensor 41. An actual air-fuel ratio (=air weight/fuel weight) during the open-loop control is calculated to calculate an estimated air excess ratioλest from a ratio of the actual air-fuel ratio to the theoretical air-fuel ratio. Presence or absence of abnormality of the alcohol concentration sensor 41 is determined based on whether or not a deviationΔλ(an absolute value) between the actual air excess ratioλdetected by the air-fuel ratio sensor 24 and the estimated air excess ratioλest is larger than an abnormality determination value. COPYRIGHT: (C)2011,JPO&INPIT
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