A head unit with built-in 4G has its own mobile data connection, just like a phone. Put a SIM card in it and the head unit can load live traffic, stream music, search for places and update its apps without borrowing a connection from your phone.
What a built-in 4G module does
Without 4G, an Android head unit gets online through Wi-Fi, usually by joining your phone's hotspot. That works, but it means switching the hotspot on for every trip, and it uses your phone's battery and data. A 4G module gives the head unit its own connection that's ready as soon as the car starts.
With a data connection, the head unit can:
- Show live traffic and search for destinations in online navigation apps.
- Stream music, podcasts and internet radio.
- Use voice search and the other online features of its apps.
- Download app updates and map updates.
- Work with online accessories, where the head unit supports them.
4G is the fourth generation of mobile networks, and LTE is the standard behind it. Coverage in the UK is good on main roads and in towns, but signal can still be weak in rural areas and some valleys, just as it is with a phone. A 4G module uses the 4G network even where 5G is available.
The 4G connection is only used for data. It doesn't replace your phone for calls, which still go through Bluetooth, CarPlay or Android Auto.
Using a SIM card for data in the car
The head unit takes a SIM card in a slot, usually on the side or the back of the unit, or on a small tray. Check which SIM size the slot needs; adaptors are available if your card is smaller. Because the slot may be behind the dashboard once the unit is fitted, it's worth fitting the SIM before the head unit goes in.
- Switch off the head unit before inserting or removing the SIM.
- Insert the SIM the right way round. The slot is usually marked.
- Switch on and go to the network or mobile data settings.
- Turn on mobile data. Most UK networks set themselves up automatically. If not, enter the network's APN details, which the network publishes on its website.
- Check that the signal bars and a 4G icon appear at the top of the screen.
The head unit also needs its 4G aerial connected and placed well. Mount the aerial high up, for example behind the top of the dashboard or the windscreen pillar trim, away from metal, for the best signal.
What to look for in a data plan
A data-only SIM is usually the most sensible choice. Things to consider:
- Data allowance. Navigation uses little data. Music streaming uses more, and video uses far more. Think about how much streaming you'll do, and check the streaming app's quality settings, which can usually be lowered to save data.
- Rolling or fixed contract. A rolling monthly SIM is easy to change if you find you need more or less data than you expected.
- Coverage. Check the network's coverage map for the roads you drive most, especially if you're often in rural areas.
- Data sharing. Some phone plans offer an extra data SIM that shares your phone's allowance. That can be simpler than a separate plan.
- Roaming. If you drive abroad, check whether the plan includes roaming and on what terms.
Be wary of SIMs that need regular top-ups or activation through a phone app. It's easier to manage the plan from your phone or a computer than from the head unit.
Getting the most from 4G in the car
- Set app updates to Wi-Fi only in the Play Store, so large updates download at home rather than over the SIM.
- Download offline maps for the areas you drive. Navigation then keeps working when the signal drops.
- Lower streaming quality in music apps if your allowance is small.
Common problems and fixes
No signal or no 4G icon
Check the SIM is seated properly and that the aerial is plugged in. Make sure mobile data is turned on and that the SIM is active; try it in a phone first if you're not sure. If the network needs manual APN details, enter them exactly as the network gives them.
Connected but nothing loads
Check the data allowance hasn't run out. Some SIMs block data until they're activated online. Restart the head unit after changing APN settings.
The connection drops on certain roads
That's usually patchy coverage rather than a fault. Offline maps keep navigation working through the gaps, and music apps can download playlists for offline listening.
Data runs out quickly
Background app updates and high-quality streaming use the most. Check the head unit's data usage screen to see which apps are responsible, then restrict them or lower their quality settings.