Ever since I upgraded to iOS 10, my phone no longer works in my car (connected over Lightning to USB port). It isn't a connectivity issue (I've received "device unsupported" before with bad connections) because the dash shows "No song" rather than "No device", but Spotify and Siri no longer run through the audio and iOS 10's (revamped) audio controls do not function. Is this an iOS 10 bug?
After much troubleshooting, the issue was the Music app being "deleted" (hidden). Even if not running the Music app—and using Spotify, Maps, etc.—the car audio does not function properly without it. Restore the app via the App Store and the car audio comes back as it was before.