Use this article if…
Use this if your MK4 is completely dead: no screen, no backlight, no boot logo, no sign it's waking at all. If you get partial life, or the volts read fine but the boot never finishes, use has power but won’t start instead.
Quick answer
If your MK4 won't power up, it's most often a low battery under load, a blown fuse or ACC/constant/earth not correct at the harness. Meter the radio plug against the PVS wiring diagram before you open the radio.
Problem
- Your MK4 won't start, loops on the logo or dies when the electrical load changes.
Symptoms
- Totally dead: you get no backlight or boot logo.
- The boot logo loops, then the screen goes black.
- It dies when you cycle the key or heavy loads hit.
- It freezes soon after you start it cold.
Cause
- Your battery is weak or the idle voltage is low.
- A plug is loose or corroded, or you're missing ACC or constant.
- A bad earth (paint-only, trailer splice).
- A blown fuse or an overloaded radio circuit.
- Accessories you've plugged into the USB are browning out the unit.
- A bad firmware image after you flashed something unofficial.
Fix Step-by-step
- Test the battery and charging with the headlights and fan on. The voltage should hold at idle.
- Re-seat every PVS harness plug, then check for bent pins.
- Meter constant, ACC and earth at the radio plug against the PVS diagram.
- Check the vehicle and inline fuses on the radio feed.
- Unplug USB hubs and dashcams from the headunit, then retest.
- Stop and contact PVS if you smell hot plastic, see melted pins or the screen stays dark with correct volts. Tell us if you flashed from USB.
Notes
- MK4 power and speaker wires
- Volts OK, no wake: Has power, won’t start
- Random reboots: Resets or freezes
No multimeter?
- Safe checks without a meter: Key off, re-seat every PVS harness plug until the latches click. Check the radio fuse isn’t blown, and swap in a same-rating spare if you have one. Unplug all USB hubs and dashcams from the MK4. Try a jump-start after a full charge, because a weak starter battery can mimic a dead headunit.
- A multimeter (or an auto electrician) is how you confirm constant, ACC and earth at the radio plug against the diagram. That’s the definitive wiring test.
- If you can’t meter: Book a short auto-electrical check, or email PVS with photos of the harness side, the fuse tap and whether the screen is completely dark or looping the logo.
Still stuck? Send us these photos
- Vehicle: model, series and year.
- Short video (10 to 20 seconds): key off, then key on. Show whether the screen stays totally black, shows only a logo loop or shows any backlight at all.
- Photos: the radio / MK4 fuse in the vehicle fuse box with the rating legible, the main PVS harness plugs at the headunit fully latched and any discoloured, melted or backed-out pins.
- Numbers (if you have them): your starter-battery voltage at idle under a normal load, for example headlights or fan. Type the exact reading in your email.
- USB / firmware: tell us whether you tried a USB update just before it failed, and use only files PVS provided, no third-party firmware.