Connecting iphone 7 to the bluetooth in my car

When you put your car into pairing mode and you tell your iPhone to pair with the car, the car will display a four digit PIN which you must enter into the phone to complete the pairing. If the car does not show this PIN on its screen, the car's default PIN will be printed in your owner's manual. Default Bluetooth PINs are quite often 0000 or 1234, as the window of opportunity for pairing with a random BT device is both small and random.

Usually the phone's bluetooth settings pops up a pin to enter into the car system or vice versa.

Nothing to do with passcode

In reality USB will be clearer and more reliable

If the car radio head is set up for CarPlay it will have a built-in USB socket. Consult your cars infotainment manual. 2012 seems a bit early for CarPlay

just checked wikipedia

"CarPlay was launched as "CarPlay" at the Geneva Motor Show in March 2014 with Ferrari, Mercedes-Benz, and Volvo among the first car manufacturers. "