When using a Volkswagen Passat 2014 and going backward, I notice that the backup camera turn off when I start gaining speed (over > ~30 km/h). How can I prevent the backup camera from turning off?
It's set in the ECU in the "Park/Steer Assist" module and controlled by an adaption channel called "Switch-off speed for parking assist" IIRC and you can change the value there (ironically jwh20 was correct in their initial guess - it's usually 15kph from the factory), the value has both lower and upper bounds that you can't go beyond (5kph -> 20kph).
This isn't something you can access through a menu in the car itself - if you want to change it you need something like VCDS, OBDeleven or Carista.
I seriously doubt those upper and lower bounds can be changed without some seriously major effort changing the firmware - and while 20kph might not sound like much, but firstly driving in reverse at speed is a bad idea in general, and trying to do it from a reversing camera view in lieu of a actually looking behind you is heading towards just plain dangerous.
I want to offer more on the frame challenge, that you just shouldn't.
What you are doing is bypassing a convenience feature that refuses to support you being more unsafe.
Start by considering what a reversing camera can't do for you. It can't give full context. You only see what a small fisheye camera (usually low down on the rear) sees - and that is not enough for safety.
For example, cams are optimised for slowish reversing, so they are fisheye/distorted. They are usually low down, and miss or de-emphasise entire risk areas at the flanks and sides. More than a short distance they distort and de-emphasise rear objects too. They miss overhanging objects (that stick out higher up perhaps). They don't show more distant objects in perspective. In fact they can't show you what's going on more than immediately behind. They mislead as to distance. They don't show lateral risks,such as dangers arriving from the sides, including for example people running from the side to go behind you.
Also these sound like places other people can go. Where wider awareness really matters at times. Driving is about risk reduction not just speed. You only need to hit one person, once, in 60 years.
Looking at a rear cam is one part of a picture. Its not all - and at any speed you're discussing, its far from enough to ensure safety.
Which brings up the other, more serious question.....
You can't reverse at speed unless reversing for some distance, and you describe the context as "large areas". Sounds like people aren't excluded from these "large areas".
If looking over your shoulder or keeping an eye on your main and side mirrors is difficult or inconvenient for a sizeable reversing manoeuvre, enough that you'd rather forcibly bypass a safety limit on the comparatively poor, limited and unsafe-at-speed rear camera, then you need to ask yourself if you are actually able to drive safely full stop, let alone at speed.
You added in a comment above, that "higher objects CAN be seen in the rear view mirror - the trunk doesn't block them. You can face forward and see BOTH the camera view and the rear view mirror, at least in my car."
Your argument here seems to be completely untenable in a safety context.
You are adamant that you indeed watch your rear view mirror anyway, at the same time, to watch for higher objects and things that are out of view of the parking cam but in view of the mirror, so these aren't a problem
Then logically you don't need the rear cam to work at speed. After all the only time you want it for reversing at speed, is a time when anything relevant visible via parking cam is as easily or more easily seen in the mirror you say you would be using to address this risk. Because it seems, your main wish in this question is to use the parking cam to avoid a wall, or other large features behind you, and all such features would be much more visible in the mirror you are also looking at, as well.
In any other case, my point about having sight of your context stands.
At the risk of getting downvotes for answering a slightly different question from what is asked, (putting aside the other not-quite-answers of "don't drive so fast" and "don't drive in reverse"), the simplest method of having a camera feed while driving your car at high speed in reverse is probably to simply buy your own camera. You probably won't be able to have it display in the built-in console, but you would be free to have it always active, with whatever field of view you choose (and you can install multiple ones for a range of views). You would even be able to see behind you when not in reverse, so this might be a useful alternative/supplement to the rearview mirror during normal driving.
Your root problem is a cognitive bias.
It's really difficult to understand "safety" when accidents happen rarely.
All minds are hardwired to learn about things by direct experience. So when something happens to you, it burns in, and you never forget it. Your mind does that automagically; even animal minds do it. The "lizard brain" as it were.
But auto accidents of a particular kind don't happen often enough for you to directly experience the consequences of mistakes.
What distinguishes humans from animals is the ability to understand risk in an abstract manner - e.g. from an NTSB safety report... From the advice of others... When the safety lesson contradicts your desires.
That is the problem. Direct experience is the only compulsory teacher. It is impossible to learn anything in the abstract unless you want to learn. Denial prevents learning.
Consider how you have reacted to the cautionary answers here. This is the "recipe for disaster": rejecting abstract safety information merely because it is inconvenient.
This doesn't mean "do not do things", it means "find the safe way to do things". I'm A-OK with high speed reversing.
You need your peripheral vision to back up safely
Because the most important information about unexpected traffic comes from beyond the fairly narrow wedge of a camera.
And the most concerning "traffic" is actually pedestrians, bicycles, skateboards, that kind of person. A person who has absolute right-of-way over you, in most cases - which means there is simply no way to escape liability for a collision.
Having to tell a court "I was nose-down in instruments, and not looking" will only be an enhancer for civil and criminal liability.
That means your head needs to be turned around full 180 degrees, shoulder twisted way over - yeah, I know the position. I once occasionally drove a railroad inspection truck. Try reversing at 60 kph for a half hour. Oh yeah, you get stiff! You won't hit any trains if everyone does their job, but hitting trespassers in an inspection car is not OK, and other inspection or MoW units may be sharing your track window.
All such movement is done on the simple rule: Be prepared to stop short of half the distance you can see. If the other person is doing the same thing, an accident is impossible. That is my axiom when driving a car, and that changes driving in surprising ways. Peripheral vision is essential to it, due to the X-factor of walkers, skateboarders, bicyclists and the like.
I'm sure it's tied in with the speedo signal from the transmission.
Being a relatively recent model I think you'll find that the display is controlled by the ECU which determines that the car is in REVERSE and is going < 30 kph. These messages are passed between the ECU and the display via the CANBUS.
To override this (safety concerns aside - let's assume you know what you're doing) you will need to do one of two things:
Intercept the CANBUS signal between the ECU and the display module and re-write the signal that says TURN-ON or TURN-OFF so that it's on when you want it and off when you don't want it. This is going to be somewhat technical so depending on your skills it may not be practical.
Intercept the speedo signal from the transmission and "fix" is so that it returns 0 when the transmission is in "R". This will take a bit of engineering as well but probably less complicated. The speedo output from the transmission should be fairly easy to find and a parts diagram of your transmission will likely show it as a replacement part. You could then find some "R" signal, perhaps from the shifting mechanism. Often there will be LEDs that light up or a switch signal that says "R".
Yes, both of these are somewhat technical but the folks at VW surely didn't consider your use-case when designing this system. In fact it's clear they intended the display to be OFF when going > 30 kph in "R".