If you download map data to your phone, it should work without mobile data. A few caveats, however.
1) You're in Android Auto. Unless you are parked, keyboard input is not allowed, so you'd have to also have offline voice recognition downloaded if you want to input an address while on the move.
2) You will not get traffic data, so routes will be 'generic' and may not be the best one depending on time/traffic conditions.
3) You would have to download all areas of your planned trip or you will lose directions as soon as you enter an area that's not in your phone.
4) Depending on where you live, some routes can be adjusted due to weather conditions. This is not available in 'offline' mode.