A computer based system on-board a vehicle configured to dynamically build and execute reconfigurable diagnostic algorithms using a pre-certified library of reusable function modules, the system comprising: a source of data that includes at least one sensed value; the library of reusable function modules in the form of precompiled code blocks which have been previously tested and verified by a certification authority, the function modules stored in the library in a machine readable format and at least one of the code blocks has an associated parameter having a user-selectable temporary value; a computer processor for executing the diagnostic algorithms in the form of a user assembled string of the code blocks; and a user interface device including a human readable display and input hardware for facilitating interaction between the user and the system to thereby: select a subset of the code blocks from the library and configure the subset of the code blocks into the user assembled string; select the user-selectable temporary value; and allocate inputs to and outputs from at least one of the subset of code blocks; an integrated reference model constructed by a processor based on the subset of code blocks, the user-selectable temporary value of the associated parameter and the allocation of the inputs to and the outputs from the at least one of the subset of code blocks, the integrated reference model includes a data sheet that provides an order of execution of the subset of code blocks, and for at least one of the subset of code blocks listed in the data sheet, the data sheet includes: the allocated inputs to and the outputs from the at least one of the subset of code blocks; the at least one sensed value from the data that is associated with the at least one of the subset of code blocks; and the user-selectable temporary value associated with the at least one of the subset of code blocks, the integrated reference model is provided by the processor to the computer processor for executing the diagnostic algorithms on-board the vehicle in the order of execution listed in the data sheet, and at run time, the computer processor receives as input the at least one sensed value from the data based on the integrated reference model, executes the subset of code blocks based on the data and the integrated reference model, and generates output values that correspond with the outputs defined in the integrated reference model. a source of data that includes at least one sensed value; the library of reusable function modules in the form of precompiled code blocks which have been previously tested and verified by a certification authority, the function modules stored in the library in a machine readable format and at least one of the code blocks has an associated parameter having a user-selectable temporary value; a computer processor for executing the diagnostic algorithms in the form of a user assembled string of the code blocks; and a user interface device including a human readable display and input hardware for facilitating interaction between the user and the system to thereby: select a subset of the code blocks from the library and configure the subset of the code blocks into the user assembled string; select the user-selectable temporary value; and allocate inputs to and outputs from at least one of the subset of code blocks; select a subset of the code blocks from the library and configure the subset of the code blocks into the user assembled string; select the user-selectable temporary value; and allocate inputs to and outputs from at least one of the subset of code blocks; an integrated reference model constructed by a processor based on the subset of code blocks, the user-selectable temporary value of the associated parameter and the allocation of the inputs to and the outputs from the at least one of the subset of code blocks, the integrated reference model includes a data sheet that provides an order of execution of the subset of code blocks, and for at least one of the subset of code blocks listed in the data sheet, the data sheet includes: the allocated inputs to and the outputs from the at least one of the subset of code blocks; the at least one sensed value from the data that is associated with the at least one of the subset of code blocks; and the user-selectable temporary value associated with the at least one of the subset of code blocks, the allocated inputs to and the outputs from the at least one of the subset of code blocks; the at least one sensed value from the data that is associated with the at least one of the subset of code blocks; and the user-selectable temporary value associated with the at least one of the subset of code blocks, the integrated reference model is provided by the processor to the computer processor for executing the diagnostic algorithms on-board the vehicle in the order of execution listed in the data sheet, and at run time, the computer processor receives as input the at least one sensed value from the data based on the integrated reference model, executes the subset of code blocks based on the data and the integrated reference model, and generates output values that correspond with the outputs defined in the integrated reference model.