One must 'open' the iPhone with the fingerprint sensor to get CarPlay to work.
You’re both partially correct. As long as the phone has been unlocked recently it can be used while locked. It’ll require face/touchID when you plug it in periodically.You can choose a setting on the phone to allow CarPlay to work when the phone is locked. They implemented this in iOS 8.3
Ha! I forgot about that feature. My phone pretty much doesn't go untouched for more than an hour while I'm awake. I feel so ashamed. lol.
Make sure you are using a quality, Apple compatible cable. I had several cables, not Apple brand, and found the one I was using was giving me trouble, and discarded. Switching to another: Works 100%!I have been unable to have the Apple car Play turn on even with my phone plugged in. It used to work but recently it doesn’t turn on.