ELM 327 Car OBD2

On-board diagnostics (OBD)  

ELM 327

ELM 327 is a OBD to RS232 Interpreter

https://drive.google.com/viewerng/viewer?embedded=true&url=https://www.elmelectronics.com/wp-content/uploads/2016/07/ELM327DS.pdf

ISO 15765 - CAN BUS

SAE J1850 BUS

The SAE J1850 bus bus is used for diagnostics and data sharing applications in vehicles.
The J1850 bus takes two forms; A 41.6Kbps Pulse Width Modulated (PWM) two wire differential approach, or a 10.4Kbps Variable Pulse Width (VPW) single wire approach. The single wire approach may have a bus length up to 35 meters (with 32 nodes).

ISO 9141 LINE

Usually in board it is connected to 

TX,RX, V+, GND to a WiFI module

In some OBD2 scanner it uses

pic18f25k80 as its chip

https://www.youtube.com/watch?v=DLKQcw506ck

Arduino Can BUS

https://www.youtube.com/watch?v=lkBILe55LQ8

Mcp2515 shield