First of all, the SSID and password should be unique. Then, you can have a QR code printed in the owner's manual, and inside the glove compartment, or something. There's a standard for QR codes for connecting to wifi, so you don't have to type in the long and cryptic password.

But I don't see much incentive to produce a fake wifi AP for me to connect to with my car diagnostics. I'm not going to punch my bank account and password into it anyway. If I'm misled to alter the battery charging settings for someone else's car, or for a pretend mockup of the car controller, I don't see what the perpetrator could gain from it.

Then there must be a button on the car dashboard, or near, which I should press to activate the AC (it does not need to be up all the time), and press again to switch it off. This can serve as an easy way to check if there's doubt. The interface may have a function like headlights on / off as a simple way to check that the connection works.