A modular influence diagram model is proposed as a decision-analytic framework for reasoning about diagnostic testing in the manufacture of mechanical products. The influence diagram ties product design, manufacturing, and testing decisions to field quality, costs and risks. The decision-analytic theory of “expected value of information” is used to evaluate the cost-benefit of alternate testing systems. The structure of the model highlights research directions for engineering economics in evaluating cost-benefit tradeoffs in the product cycle from design, to manufacturing, marketing and field service. An implementation in the IDES (Influence Diagram Based Expert System) illustrates the potential of applying such a planning model to real-time diagnostic decisions in the manufacture of mechanical components for high-speed printers.