RESPONSIVENESS DETERIORATION DIAGNOSIS DEVICE FOR EXHAUST GAS SENSOR

PROBLEM TO BE SOLVED: To prevent erroneous diagnosis of air-fuel ratio sensor responsiveness deterioration by brake operation. SOLUTION: An intake pipe negative pressure type brake booster 26 for increasing braking force of a brake is connected to an intake pipe 12. When a driver operates the brake and the brake booster 26 is operated, the intake pipe negative pressure is varied, and an actual air-fuel ratio is varied. When the responsiveness deterioration diagnosis of an air-fuel ratio sensor 32 is executed just after the driver operates the brake, there is a possibility that the responsiveness deterioration of the air-fuel ratio sensor 32 is erroneously diagnosed by variation of the air-fuel ratio caused by brake operation. As a measure, in a predetermined time period after brake operation start (off-state to on-state) is detected by a brake switch 29 and a predetermined time period after brake operation end (on-state to off-state) is detected, responsiveness deterioration diagnosis of the air-fuel ratio sensor 32 is forbidden. Thus, the erroneous diagnosis of the responsiveness deterioration of the air-fuel ratio sensor 32 by brake operation can be prevented. COPYRIGHT: (C)2007,JPO&INPIT