Patent ID: 8594906

Claim:
A method of diagnosing an internal combustion engine system having a multi-cylinder internal combustion engine and an air fuel ratio sensor which detects an air fuel ratio of mixed exhaust gas flowing from the multiple cylinders and outputs a signal corresponding to said detected air fuel ratio, the method comprising: for each of a plurality of diagnostic control loops: for each of a predetermined number of sub-cycles of a combustion cycle of the engine: at a powertrain control module, receiving air fuel ratio data as input data from the air fuel ratio sensor; computing a square value of a difference between a beginning output value and an end output value of the input data, said air fuel ratio sensor outputting the beginning output value and the end output value at discrete timings within each sub-cycle; integrating said square value during each sub-cycle; and after the predetermined number of sub-cycles; diagnosing said internal combustion engine system based on said integrated square value to determine whether a computed integrated value R 1 exceeds a threshold value which is set in advance; if the R 1 value exceeds the threshold value, determining that an abnormality exists in the diagnosis for the diagnostic control loop; computing a rate of abnormalities detected among the plurality of diagnostic control loops, and after the plurality of diagnostic control loops: determining whether the rate exceeds an abnormality determination value set in advance; and if the rate exceeds the abnormality determination value, then outputting an alarm to a diagnostic indicator.