The recent improvements in automotive electronics have had a tremendous impact on safety, comfort and emissions. But the continuous increase of the volume of electronic equipment in cars (representing more than 25% of purchasing volume) as well as the increasing system complexity represent a new challenge to quality, post-sales customer support and maintenance. Identifying a fault in a complex network of ECUs, where the different functions are getting more and more intricate, is not an easy task. It can be shown that with the levels of reliability common in 1980, an upper-range automobile of today could never function fault-free. On-Board-Diagnostics (OBD) concepts are emerging to assist the maintenance personnel in localizing the source of a problem with high accuracy, reducing the vehicle repair time, repair costs and costs of warranty claims. Further benefits are an early warning to the driver, who can then take corrective measuresBased on network and system models and learning algorithms, microcontrollers are taking over diagnostics, failure identification and even prevention. Software incorporates all the rules for acting and reacting to the system status and providing limp home functionality wherever possible. In order to reliably and identify a failure, more detailed status information on the network and the individual nodes is needed. Potential causes for failures, such as overvoltage, overtemperature, overcurrent, etc. need to be monitored to prevent damage. When a fault occurs to be identified accurately and signaled to the system's brain with minimal latency. Sensing the relevant signals and physical parameters, though, adds to the system costs and complexity. Recent advances in smart power semiconductors open new ways of integrating the diagnostics functions needed for signal sensing, communication and self-protection in a very cost-efficient way. This paper discusses the actual situation and advanced possibilities of diagnostic and control functions in Automotive Power Electronics and shows how smart technologies and architectures can efficiently contribute to improve reliability, quality and safety of passenger cars.