Use this article if…
Pick your symptom (one line): Black or “no signal” (reverse opens but no video) · Never switches off radio / maps · Picture wrong but not blank (rolling, tinted, scrambled, fuzzy), use Fix on this page.
- Use this overview article if: you need the MK4 camera fault overview, wrong or distorted image with video present, intermittent camera after bumps, loose-adapter suspicion, or multi-step AHD/CVBS + trigger + LC76 / 28‑pin context in one place.
- Do not use this as your first stop if: the reverse screen opens but the image area is only black / blank / “no signal” → Reverse camera shows black screen.
- Do not use this as your first stop if: reverse never opens a camera page (you stay on radio, maps, or the last source) → No reverse camera showing when in reverse.
- Parking / trajectory lines missing with otherwise OK video → Parking guidelines missing.
- Not an MK4 headunit → Black / wrong picture (generic) · Cameras hub.
Quick answer
Triage first: black or “no signal” with the camera page open goes to the black-screen guide; no switch from radio/maps goes to the no-display guide; this overview covers wrong or rolling pictures, intermittent faults, and the full adapter/trigger/format checklist.
Problem
- Reverse or extra camera will not switch on, or the picture is wrong.
Which article? Black / blank / “no signal” with the camera layout visible → Reverse camera shows black screen. Never leaves the previous source in reverse → No reverse camera showing when in reverse. Live picture but distorted (rolling, colours, interference), stay on this page and use Fix.
Symptoms
- Black screen only in reverse - other sources fine.
- Camera never switches; you only see the last source.
- Rolling, tinted, or scrambled image.
- Works cold, fails after a bump (intermittent).
Cause
- Reverse trigger wire missing or reading low (PWM tail-light tap, bad ground).
- Adapter harness (e.g. 28-pin conversions) partly unplugged or pin-damaged.
- Trailer/loom grounds sharing the reverse circuit.
- Rare: camera body failed while radio still good.
Fix Step-by-step
- Open camera settings and flip between AHD and CVBS to match your camera type; reboot once after changing.
- With wheels chocked and brakes set, meter the reverse input at the MK4 loom while selecting reverse - expect solid activation per your diagram.
- Reseat every adapter shell; look for backed-out terminals.
- Swap camera inputs temporarily (where safe) to prove a specific port works.
- Clean shared earth points if you tow with an aftermarket harness.
Notes
- Install wiring: How to wire cameras to the MK4
- No switch in reverse: No reverse display
- Black / wrong picture: Reverse black screen
- Picture OK, no parking lines: Parking guidelines missing
- Trigger theory: Reverse trigger wiring, AHD vs CVBS
- Harness power: MK4 harness
No multimeter?
- Safe checks without a meter: Toggle AHD/CVBS to match the camera, reboot once; re-seat every adapter shell; confirm reverse input assignment in settings; swap the camera feed to another allowed input to test the port (helper in reverse, vehicle safe).
- A multimeter is required for the “prove reverse trigger at the loom” step - needed when the screen never switches or the trigger is suspected marginal (PWM tails, trailer looms).
- If you can’t meter: Finish format/adapter seating first; for pure-black with a camera page use Reverse black screen; for no switch at all use No reverse display - then an installer trigger test or PVS email with video plus adapter photos.
Still stuck? Send us these photos
- Vehicle: model, series, and year.
- Short video: chocked, brakes on - shift into reverse twice; show whether the UI switches and what the picture does.
- Screenshots: MK4 camera format menu (AHD/CVBS) and reverse input assignment / multiview page.
- Photos: every adapter shell or 28‑pin conversion between camera loom and headunit - both sides, plugs latched.
- Camera: brand or part number on the camera body / box if visible.
- Say which branch matches: black screen vs no switch vs wrong picture - so we do not re-route you in email.