DIAGNOSTIC DEVICE FOR SECONDARY AIR SYSTEM OF EXHAUST EMISSION

摘要

PROBLEM TO BE SOLVED: To prevent an erroneous diagnosis at a highland where a suction negative pressure is reduced. SOLUTION: An air-cut valve 71 is opened when suction negative pressure is introduced to open a secondary air supply passage to the upstream of a catalyst and is closed when atmospheric pressure is introduced to close the secondary air supply passage. The introduction of the suction negative pressure or the atmospheric pressure to the air-cut valve 71 is exchanged by exchange means 72 and instructing means 73 instructs the exchange means 72 to introduce the suction negative pressure to the air-cut valve 71 while increasing the amount of fuel when an engine is started at low temperatures. Judgment means 74 judges if the secondary air flows to the upstream of the catalyst or not during this instruction and when the judgement means 74 judges that the suction negative pressure to the air-cut valve 71 is less than target figures, judgement prohibiting means 76 prohibits judging whether the secondary air flows or not.