First, you have to connect your i.MX6 board to the CAN bus of the OBD-II connector:
https://en.wikipedia.org/wiki/On-board_diagnostics
Then, you have to study the OBD-II protocol:
https://en.wikipedia.org/wiki/OBD-II_PIDs
And then you have to start entering PIDs from the processor and receiving parameters from the car's ECU and other systems.
You can google much more in the internet on that matter.
Have a great day,
Artur
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