Use this article if…
Use this if you're reading the right supply at the plug, or you see a backlight or logo, but the screen stays black or Android never fully loads. If you get no sign of power at all, start with won’t turn on / restarts. If it boots then locks up or reboots while you're driving, use resets or freezes.
Quick answer
If you get lights but Android never finishes booting, unplug every USB add-on. Check that both constant and ACC are right on the main harness. Then give it one long first boot before you call it a hardware fault.
Problem
- You've got power at the plug, but the screen stays black or the boot never finishes.
Symptoms
- You measure correct supply at the plug, or the cabin lights prove the circuit lives, but the screen stays black.
- Or you see the logo once, then the boot never finishes.
- This isn't everything stone dead: you can see signs the unit is partly awake.
Cause
- You've got ACC and constant at the harness that don't match the diagram, so the unit part wakes without a healthy boot supply.
- A USB device or hub you've plugged in is hanging early USB enumeration before Android finishes booting.
- A long first-boot optimisation or storage maintenance stalls, and you read it as a fault.
- Corrupted firmware or an unofficial image you flashed left the system partition inconsistent.
Fix Step-by-step
- Confirm both constant and ACC behave as per the harness diagram with the ignition on, not just battery voltage at one pin.
- Unplug every USB accessory from the headunit, then long-press power if your build has a hard key (per quick-start).
- Leave the ignition on for several minutes once to rule out a first-boot optimisation stall, then key cycle.
- If it started right after you copied files from an unknown source, stop and email PVS before you flash 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 the ignition on several minutes once for first-boot optimisation, then key off and on; re-seat the main loom plugs; confirm the wire positions still match the printed diagram (no pins swapped by a previous installer).
- A multimeter is what you need to confirm ACC goes live and off with the ignition and that constant stays present. Partial voltage can look fine until you check both pins under the right key states.
- If you can’t meter: Carry on with the USB and re-seat steps, then get an auto electrician to do a 10-minute harness verify, or email PVS describing the key positions, backlight or no backlight, and any USB update you ran before it failed.
Still stuck? Send us these photos
- Vehicle: model, series and year.
- What you see: a short video of the key cycles, noting backlight only, a frozen logo, or black glass after the logo.
- Confirm: you've unplugged every USB device from the MK4 for this test, and say so in the email.
- Photos: the main harness at the headunit with the plugs latched, and the fuse position if you think it's a radio-circuit fault.
- Meter notes (if available): constant and ACC at the radio plug with the key off and the key on, written against the PVS diagram labels.
- USB / firmware: whether you flashed an unofficial or non-PVS USB image before the problem started.