Modern investment goods such as commercial vehicles show a rise in complexity due to an increase in mechatronic elements. As a result, such products are more sensitive to defects, often reflected in reduced reliability during product usage. Therefore, reliability is a quality feature that is gaining more importance throughout the entire product life cycle (PLC). However, rather than considering the complete PLC, traditional quality assurance techniques typically focus on individual life cycle phases. The following paper thus proposes a new approach for closing the resulting gap. Adapting a technique originating from the domain of software engineering for the life cycle of mechatronic products enables a consistent classification of product defects. Based on this classification, proper means for quality improvement can be developed and implemented. Consequently, an evolutionary increase in reliability becomes possible.