Abstract: Disclosed is a system and method which systematically diagnoses emissions test failure by applying the rules of a knowledge base to predict the cause of vehicle emissions failures. Classifiers are used to form predictions. The classifier is the data structure used in the automobile emission testing inspection lane by the lane diagnostic subsystem to provide a diagnosis for a particular vehicle. Its output is the likelihood that a vehicle suffers from a given failure based on the values of characteristics such as its emissions test results and the vehicle's description. The classifier predictions are then used to prepare a failure report that is given to the motorist for use by his or her repair technician. In another feature of this invention, the classifiers are continuously updated in a learning process based on new repair records. The learning processes periodically analyzes the data and updates the knowledge base to include new or revised classifiers.

Abstract: The combination of ambient air, exhaust and premeasured calibration gases is used according to this invention in the analysis of either low or high pollutant concentration gases measured by a single range analyzer. By using ambient air as a diluent and employing its concentration values to generate the Reference Dilution Ratio, DR.sub.ref, iterative calculations are made to find the Raw Sample Concentration value, C.sub.raw. The gas diluting/mixing system includes pressure balanced infeed plumbing legs. Each of the legs feeds to respective flow restrictors and a common, downstream mixing "T" fitting. One leg is interconnected to the high concentration emission gas output from the sampling system and high concentration calibration gas. The other leg is interconnected to the diluent gas source, ambient air.