Use this article if…
Use this if the unit is completely dead - no screen, no backlight, no boot logo, no sign the MK4 is waking at all. If it shows partial life or voltage is good but boot never finishes, use has power but won’t start instead.
Quick answer
A unit that will not power up is most often 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 opening the radio.
Problem
- MK4 will not start, loops on the logo, or dies when electrical load changes.
Symptoms
- Totally dead: no backlight or boot logo.
- Boot logo loops, then black.
- Dies when key cycles or heavy loads hit.
- Freezes soon after cold start.
Cause
- Weak battery or low idle voltage.
- Loose or corroded plugs; missing ACC or constant.
- Bad earth (paint-only, trailer splice).
- Blown fuse or overloaded radio circuit.
- USB-powered accessories browning out the unit.
- Bad firmware image after an unofficial flash.
Fix Step-by-step
- Test battery and charging with headlights and fan on - voltage should hold at idle.
- Re-seat every PVS harness plug; check bent pins.
- Meter constant, ACC, and earth at the radio plug vs PVS diagram.
- Check vehicle and inline fuses on the radio feed.
- Unplug USB hubs and dashcams from the headunit; retest.
- Stop - contact PVS if you smell hot plastic, see melted pins, or the screen stays dark with correct volts. Say if you flashed from USB.
Notes
- MK4 power and speaker wires
- Volts OK, no wake: Has power, will not start
- Random reboots: Resets or freezes
No multimeter?
- Safe checks without a meter: Key off, re-seat every PVS harness plug until latches click; confirm the radio fuse isn’t blown (swap in a same-rating spare if you have one); unplug all USB hubs/dashcams from the MK4; try a jump-start after a full charge - a weak starter battery mimics a dead headunit.
- A multimeter (or auto electrician) is required to verify 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, fuse tap, and whether the screen is completely dark vs logo-loop.
Still stuck? Send us these photos
- Vehicle: model, series, and year.
- Short video (10–20 s): key off → key on - show whether the screen stays totally black, shows only a logo loop, or any backlight at all.
- Photos: radio / MK4 fuse in the vehicle fuse box (rating legible); main PVS harness plugs at the headunit fully latched; any discoloured, melted, or backed-out pins.
- Numbers (if you have them): starter-battery voltage at idle with a normal load (e.g. headlights or fan), type the exact reading in your email.
- USB / firmware: state whether a USB update was attempted just before failure and use only files PVS provided - no third-party firmware.