Here is a basic introduction to the OBD II communication protocol.
Mode byte: The first byte in the stream is the mode number. There
ar 9 modes for diagnostic requests, so this first byte is from 1 to 9.
The first byte in the response data bytes is this same number plus 64.
For example, a mode 1 request would have the first data byte = 1,
and the response would have the first data byte = 65.
2. Using the Scan Tool
• Tool Description
①
OBD II CONNECTOR
– Connects the scan tool to the vehicle's Data
Link Connector (DLC).