Use this article if…
Use this if supply at the plug looks right (or you see backlight/logo) but the screen stays black or Android never fully loads. If there is no sign of power at all, start with won’t turn on / restarts; if it boots then locks up or reboots while driving, use resets or freezes.
Quick answer
If lights come on but Android never fully boots, disconnect all USB add-ons, confirm both constant and ACC are correct on the main harness, and allow a long first-boot wait once before assuming hardware fault.
Problem
- Power is present at the plug but the screen stays black or boot never finishes.
Symptoms
- You measure correct supply at the plug (or cabin lights prove the circuit lives), but the screen stays black.
- Or the logo appears once, then never finishes boot.
- Differs from ‘everything stone dead’ - there are signs the unit is partially awake.
Cause
- ACC and constant behaviour at the harness do not match the diagram - partial wake without healthy boot supply.
- A USB device or hub is hanging early USB enumeration before Android completes boot.
- Long first‑boot optimisation or storage maintenance stalls that look like a fault.
- Corrupted firmware or unofficial image flash left the system partition inconsistent.
Fix Step-by-step
- Confirm both constant and ACC behave per the harness diagram with ignition - not just battery voltage at one pin.
- Disconnect every USB accessory from the headunit and long‑press power if your build has a hard key (per quick‑start).
- Leave ignition on for several minutes once to rule out first‑boot optimisation stalls - then key cycle.
- If the problem began right after copying files from an unknown source, stop and email PVS before flashing again.
Notes
- Full power checks: Won’t turn on / restarts
- Harness: MK4 wiring
- Reboots after boot: Resets or freezes
- Wizard: First-time setup
No multimeter?
- Safe checks without a meter: Remove every USB device from the MK4; long-press power if your build has a hard key; leave ignition on several minutes once for first-boot optimisation, then key off/on; re-seat the main loom plugs; confirm wire positions still match the printed diagram (no pins swapped by a prior installer).
- A multimeter is needed to confirm ACC goes live/off with ignition and that constant stays present - partial voltage often looks “fine” until both pins are checked under the right key states.
- If you can’t meter: Continue with USB/unseat steps, then use an auto electrician for a 10‑minute harness verify, or email PVS describing key positions, backlight vs no backlight, and any USB update before failure.
Still stuck? Send us these photos
- Vehicle: model, series, and year.
- What you see: short video of key cycles - note backlight only, frozen logo, or black glass after logo.
- Confirm: every USB device unplugged from the MK4 for this test (say so in the email).
- Photos: main harness at the headunit (plugs latched); fuse position if you suspect a radio-circuit fault.
- Meter notes (if available): constant vs ACC at the radio plug with key off and key on - write the values against the PVS diagram labels.
- USB / firmware: whether an unofficial or non-PVS USB image was flashed before the problem started.