Since 1996, most vehicles have been required to monitor their own emissions performance and to report on it through an On-Board Diagnostics (OBD) port. Initially, several different protocols were used for the transfer of OBD data, but since the 2008 model year (in North America), only one protocol is now allowed - the ISO 15765-4 CAN standard. The ELM329 is a device that can translate the data from an ISO 15765-4 interface into a form that may be readily used by computers, smart phones, or other devices. In addition, it provides support for other CAN protocols (including the SAE J1939 truck and bus standard), for mixed ID data sending, for monitoring of the CAN bus, and for other features such as high speed computer communications, and a low power sleep mode. The following pages discuss all of the ELM329 s features in detail, how to use it and configure it, as well as providing some background information on the protocols that are supported. There are also schematic diagrams, tips to help youto interface to microprocessors, and to construct a basic scan tool.