Q: my 4s no longer talks to my car when I get in, what is wrong

Without knowing anything about the car it's almost impossible to answer your question. Usually when this happens you can get in the car, turn it on, then, on the iPhone, go to Settings/Bluetooth and tap the name of the car system to connect.

If the car's name is not in the phone the pairing has been lost; you need to put the car in pairing mode (you will have to consult the car's manual, as every car is different) and re-pair the car and the phone.