Engine Control Systems (ECS) for automobiles have numerous variants for many manufactures and different markets. To improve development efficiency, exploiting ECS commonalities and predicting their variability are mandatory. The concept of software product line engineering meets the business background of ECS. However, we should carefully investigate the expected technical, economical, and organizational effects of introducing this strategy into existing products. This paper explains an approach for assessing the potential of merging existing embedded software into a product line approach. The definition of an economically useful product line approach requires two things: analyzing return on investment (ROI) expectations of a product line and understanding the effort required for building reusable assets. We did a clone analysis to provide the basis for effort estimation for merge potential assessment of existing variants. We also report on a case study with ECS. We package the lesson...