The full name of UDS is Unified Diagnostic Services. For the detailed description and definition of UDS, you can refer to the series of documents of the ISO 14229 standard for in-depth understanding. The reason why the UDS function has been emphasized is more important and basic, because the USD function has a direct impact on many other functional modules and basic operations in the process of vehicle production and use. First of all, when the vehicle production line is offline, the production line electric inspection will use the electric inspection instrument to write a lot of necessary preset value information to multiple ECUs through UDS, such as writing the VIN code, part number, logistics information, etc. of the corresponding vehicle, and also Some specific settings can be activated, or some specific states can be locked to prevent random changes of components, etc. When the vehicle is maintained at the 4S shop, the upgrade of ECU firmware, the reading and elimination of fault codes, etc. are also completed through the OBD port connection and UDS related services. As we mentioned in the previous article, the communication between devices on the CAN network can basically be divided into three situations, namely: the device periodically actively sends some status messages; a certain condition changes and meets the set requirements, thereby passively Trigger-type signaling; query and reply-type signaling.