OBD-II

Freematics OBD-II UART Adapter V1 (for Arduino)

https://github.com/stanleyhuangyc/ArduinoOBD

http://freematics.com/store/index.php?route=product/product&path=20&product_id=30

A cable coming out from the adapter splits into two 2-pin Dupont connectors with one for power (VCC/GND) and one for data (Rx/Tx). They are connected to Arduino to provide both power supply and data connection. Your Arduino setup will look tidy in car with only one cord.
Power Lines:
•Red: VCC (connecting to Arduino's 5V/VCC)
•Black: GND (connecting to Arduino's GND)
Data Lines:
•White: Rx (connected to Arduino’s serial Tx)
•Green: Tx (connected to Arduino’s serial Rx)
 
https://www.sparkfun.com/datasheets/Widgets/ELM327_AT_Commands.pdf
https://en.wikipedia.org/wiki/ELM327

Freematics OBD-II I2C Adapter (for Arduino)

https://freematics.com/store/index.php?route=product/product&path=20&product_id=51

https://github.com/jrowberg/i2cdevlib

Power Lines:
•Red: VCC
•Black: GND
Data Lines:
•Green: SDA
•White: SCL
I2C Addresses:
•OBD I2C Address: 0x68
•MEMS I2C Address: 0x62

38400 8 1 N
ATI
OBDUART v1.0<\r><\r>>
4F 42 44 55 41 52 54 20 76 31 2E 30 0D 0D 3E
079 066 068 085 065 082 084 032 118 049 046 048 013 013 062

Freematics Mega Kit (Arduino Mega based)

https://freematics.com/store/index.php?route=product/product&product_id=58

https://freematics.com/pages/products/arduino-telematics-kit-3/developers-guide/

https://freematics.com/store/index.php?route=product/product&path=59&product_id=70

OBD-II PIDs

https://en.wikipedia.org/wiki/OBD-II_PIDs

ELM327

https://en.wikipedia.org/wiki/ELM327
https://www.sparkfun.com/datasheets/Widgets/ELM327_AT_Commands.pdf
https://www.elmelectronics.com/wp-content/uploads/2016/07/AT_Command_Table.pdf

https://www.youtube.com/watch?v=cAAzXM5vsi0