The product dimensional quality could be affected by multiple error sources in manufacturing processes. One widely observed engineering phenomenon is that different error sources can result in identical error patterns on product features. For example, deviations in fixture locators and workpiece datum surfaces can produce the same type of dimensional variations in engine head machining. Such an "error equivalence" phenomenon often significantly increases the complexity of dimensional variation control such as root cause identification. By generalizing and extending the authors' previous work, the paper aims to establish error equivalence methodology which addresses issues of mathematical modeling of the error equivalence phenomenon in manufacturing, error equivalence analysis for root cause identification and automatic adjustment.