ELM-327

If you are working with cars and trying to diagnose it, at some point you will need to interface onboard computer into computer. 
Here we offer an OBD-II to serial emulator. It provides simple serial TTL level voltages that you will need to connect to some sort of converter to interface it into RS232, USB or Bluetooth

PCB layout with DB9  will require  cable  with DB9 to vehicle's OBD-II J1962 connector. or alternative layout with male OBD connector. 

For more information, refer to:    http://PCBhut.com/Products/ELM327/index.html