Embodiments of the invention generally relate to weighing scale diagnostic methods employing a comparison of like component operating parameters. In certain embodiments, the difference between any two current operating parameter values may be compared against a maximum allowable difference, and/or the deviation of current operating parameters from a calculated measure of central tendency may be determined and compared against a maximum allowable deviation. Alternatively or additionally, a standard statistical test for outliers may be employed. An outlying difference or deviation may be indicative of a problem with the associated component. In other embodiments, the current operating parameters of like components may be compared against calibrated parameters and any deviation of the current parameter for a given component may be compared against the total deviation to determine the percentage of deviation attributable to that component.