This. The legislated application layer which must be present requires that the control module be addressed and specific data requested. While you might have e

This. The legislated application layer which must be present requires that the control module be addressed and specific data requested. While you might have experience with a modern car that broadcasts some of the data interested by the dongle, this is not universal. Where this happens it may be on a different network segment than what you access physically on the OBD2 connector. There may or may not be a gateway between networks in the car, and it may or may not need to be activated, which is not part of the universal application mandated by CARB/EPA. In addition the dongle may be interested in some information that may not be broadcast. For instance the instrument cluster should receive periodic updates about the current road speed. However it's less likely that something I'd be interested in if I were an actuary is broadcast: the throttle position! While the universal CARB/EPA application cannot generally command control modules, this dongle has access to the PHY and could send packets that correspond the manufacturer-specific applications that could be dangerous while a motor vehicle is in operation. With the UART based and PWM protocols that preceded CAN, there were some nuances with the manufacturer-specific protocols on those PHYs that did not line up with the CARB/EPA mandate, so the more generic gateways will not be able to construct these kinds of messages. Now, everything is plain CAN, there is nothing strange about it like "tickle the auxillary line with the destination address at 5 bps to wake up that module." Any CAN node will do.