A controller area network bus is a communications system used in modern automobiles to connect the electronic control units that implement normal vehicular operations as well as advanced autonomous safety and driver comfort features. However, these advancements come at the expense of vehicle security – researchers have shown that automobiles can be hacked by compromising electronic control units or by connecting unauthorized devices to the controller area network bus.Physical layer device fingerprinting is a promising approach for implementing vehicle security. This chapter presents a fingerprinting method and classification algorithm for electronic control unit discrimination. Cross-lot discrimination is assessed using four Toyota Avalon electronic control units with different lot numbers as authorized devices, and a BeagleBoard, Arduino and CANable as rogue devices. The experiments yielded perfect rejection rates for rogue devices with false credentials and access denial rates exceeding 98% for authorized electronic control units with false credentials. Additionally, an average correct classification of approximately 99% was obtained for authorized devices.