AIR/FUEL RATIO SENSOR FAILURE DIAGNOSTIC DEVICE

摘要

A failure diagnostic device calculates a calculation air/fuel ratio A/Fk from the amount of fuel injected and the amount of air sucked and judges if an air/fuel ratio sensor fails or not on the basis of the calculation air /fuel ratio of when the operating state of an internal combustion engine relatively sharply varies in response to an engine operation request and thereby the calculation air/fuel ratio relatively sharply varies and the actual air/fuel ratio A/Fr detected by the air/fuel ratio sensor. Since the air/fuel ratio is not forcedly changed/varied, deterioration of the exhaust emission and combustion state at the failure diagnosis and vibration, noise, and so forth can be reliably prevented.