How to Fix iOS 11/11.1/11.2/11.3 CarPlay Not Working?
Tip 1. Update to the latest iOS 11.3
Tip 2. Check if you have turned on Siri
You cannot make voice commands without Siri. Go to Settings > Tap Siri & Search > Turn it on.
Tip 3. Check your Restrictions
Open Settings app > Tap General > Restrictions > Enter your passcode > Find CarPlay and turn it off.
Tip 4. Reset your iPhone
First restart your iPhone to have a try, press and hold down the Power button > Drag slide to power off. If it doesn’t work, you can hard reset your iPhone to fix the CarPlay not working in iOS 11 issue.
For iPhone 6s and earlier iPhone: press and hold down the Home button and the Power button together until you see the Apple logo on screen.
For iPhone 7/7 Plus: press and hold down the Home button and the Volume Down button together.
For iPhone 8/X: first press and quickly release the Volume Up button, then press and quickly release the Volume Down button, finally press and hold the Power button until the Apple logo appears.