The automobile industry's rapid growth enables developments in all branches of the sector. This also includes electronics, where the latest technological nodes are used today. New challenges to providing safety and reliability for such circuits are thus to be faced. One of these is the diagnostics of analog and mixed-signal circuits. Performing failure analysis has become very difficult indeed, due to the lack of auto-diagnosis methods. This paper describes a solution to improve the diagnosis of such circuits. We can insert elementary devices that return circuit states via light emission by utilizing the basic principles of light emission from silicon electronic components. These elementary devices are used to check every fundamental signal of the circuit, with significant benefits for diagnostics and failure analysis. All actions leading from concept to real silicon are explained. The reported results for a real silicon circuit and a failure analysis case demonstrate the effectiveness of this method.