Android Auto Black Screen? Find the Layer That Lost the Picture

A black screen has a short list of causes, and they sort cleanly by where the picture stops. Run the fast pass first — it clears most cases. If it survives, jump to the section that matches your symptom.

The fast pass

1. Swap to a known data cable and another USB port. Charge-only cables are the single most common cause.
2. Reboot both ends — phone and head unit.
3. Update Android Auto. Current releases (16.7+) need Android 12L or newer — on older Android they won't even install.
4. On wireless? Test once over USB to split the problem in half.
5. Mirroring with KoalaMirror? Run the in-app health check and fix the one item it flags.

The car never shows Android Auto

• Switch the head unit's source to Android Auto — some units also keep a master toggle, off by default.
• Exempt Android Auto from battery optimization — aggressive managers (Samsung One UI's sleeping-apps list, for example) kill it in the background.
• Wireless: Bluetooth on, 5 GHz Wi‑Fi free. If the phone is pinned to another network, the handshake dies silently. Re-pair from scratch if in doubt.
• Android 14: give the first connection a minute. It runs an extra permission check that must time out on its own — we've measured this; don't pull the plug at twenty seconds.

Connected, but the screen stays black

• Clear Android Auto's cache — the safe reset after an update.
• Custom ROM? Check Google services first, not the cable. Android Auto builds the car UI on Google Mobile Services. In our device testing, a GMS‑less ROM connected end to end and rendered nothing; a minimal GApps package on the same phone brought the picture up.

Mirroring a desktop? Two causes stock guides never see

• No home screen on the projected display. It's a real Android display — with no launcher on it, there is nothing to draw, and black is exactly what "nothing" looks like. Set a car-friendly one; KM Launcher is free and built for this seat.
• Deployed, but never rebooted. The projection module only activates after a restart — until then everything looks installed and nothing runs.

KoalaMirror's built-in health check walks this exact layer — root grant, module active, Google services, Android Auto version, launcher — and names the failing item instead of leaving you to guess.

It worked yesterday

• Something updated — phone OS or Android Auto. Check both before suspecting hardware.
• KoalaMirror's safety fuse tripped. Repeated boot-time crashes auto-disable the module to protect the phone; re-deploy re-arms it, and the health check calls this state out.
• A reboot is still pending from an earlier update or re-deploy.