Patent ID: 7389637

Claim:
Diagnostic equipment for an exhaust gas cleaning apparatus for an engine system furnished with an air-fuel-ratio controller which detects an air fuel ratio of exhaust gas emitted from an engine and which adjusts a quantity of fuel injection so as to hold the air fuel ratio of the exhaust gas at a predetermined value, and a catalyst for cleaning said exhaust gas; comprising: an air-fuel-ratio sensor which detects the air fuel ratio of the exhaust gas upstream of said catalyst; a catalyst-deterioration-index calculation means for calculating a catalyst deterioration index indicative of a deterioration state of said catalyst from output signals of said air-fuel-ratio sensor; a catalyst-deterioration decision means endowed with a predetermined threshold value for deciding the deterioration state of said catalyst through a comparison between the threshold value and the catalyst deterioration index; an abnormality detection means for detecting any abnormality of said engine system affecting said catalyst deterioration index as when a spiked-shaped signal which points out a lean side is outputted from the air-fuel-ratio sensor; and a catalyst-deterioration-decision interruption means for interrupting the decision of said catalyst-deterioration decision means when the abnormality has been detected by said abnormality detection means.