4G LTE sim for Android Auto internet

In order to get Internet into my Android Auto head unit, I will need a suitable sim card with data.
Would I be able to utilise some of my existing data allowance or would a new contract be necessary?
Are there any other ways of doing that?
Many thanks
Martin

MartinH2 does the Android Auto head unit use it's own SIM or does it connect via your phone?

Android Auto units use the WiFi connection to the phone for streaming music and maps. But Internet will require another sim and a dongle as far as I can tell.
Thanks for getting back.