The aim of the study is to identify the causes of non-compliance of castings and ultimately, using quality management tools (5W2H I diagram Ishikawa), to reduce or eliminate the number of such non-compliance. The research was carried out using visual, luminescence and metallographic tests and the product was a diesel engine piston casting. The study identified clusters of rows in the area of sealing canals and specified their cause -inadequate quality of the charge. So far, no analyses of quality problems using a sequential quality management methodology have been carried out in the company, so that the implemented corrective actions did not lead to the full achievement of quality objectives. The sequential method presented in the paper, combining diagnostic and control tests and quality management tools, is a universal way to monitor the quality level of products and to quickly correct any nonconformities. The presented method can be used in enterprises producing products from ferromagnetic, non-ferromagnetic and non-metallic materials (due to the effectiveness of the luminescence method).