On Board Diagnostic Connector: OBD2 connector, location and tests

The OBD2 connector is used to connect the car's computer with an external phone, external computer or external scanner in order to diagnose engine and car faults in general.
The OBD2 connector has a trapezoidal shape or "D" shape with 16 pins, of which No. 4 and No. 5 are used as electrical ground, No. 16 terminal as 12V power terminal.
Depending on the protocol used, the OBD2 connector has one of the following terminal pairs:
2 and 6 J1850 protocol
6 and 14 CAN protocol
7 and 15 ISO 9141 or ISO 14230 protocol.