Car control via CAN bus?

I once saw that you can do a lot with the CAN bus in a car.
Is it theoretically possible that I read out the corresponding signals that are needed, for example, to control the high beam, etc., and then repeat them via the laptop in order to control my car?

I'll keep thinking that I want to build an "on-board computer" like in the Tesla.
I would program my own speedometer, etc.

I work in special vehicle construction and have a very extensive diagnosis / service tool for our vehicles.

Some components are integrated in the CanBus but can't be read out in order to parameterize them (assign numbering so that the vehicle can start something) you have to import a binary code into the CAN bus.

As diagnostic hardware we use a CAN to USB sandler called "ixxat usb-to-can" together with a company's own software and diagnostic cable harness with which I can also hang myself directly on control units.

You can control certain things. Requirements for fading in the high beam come from the vehicle buses, including horns, indicators, washer fluid, radio controls from the steering wheel, everything is done quite openly via vehicle bus systems (not only CAN, but also LIN and Ethernet). Mostly harmless things.

Which normally shouldn't work once the vehicle manufacturer has done its homework: braking, accelerating, steering.

To do this, you usually first have to hack your way through the individual vehicle control units step by step until you have reached the point actually controlling.

So for the brake you have to change the software on the control unit that executes the ESP at some point.

For the steering wheel, you can theoretically use the servomotors for self-steering parking systems in today's cars.

To accelerate you have to crack the engine directly.

In theory, complete remote control is conceivable, but not practical. However, individual functions work without any problems.

As someone who has already worked professionally with vehicle networks, for example, I have of course allowed myself the fun of starting the windscreen washer pumps from a distance while someone else is working on the car.

Oha. Thank you for the detailed answer.
I'll try a few things out there.

Cool cool.
Thank you for your detailed reply.
I hope I can make something small, and if it's just a party gag that the car is going crazy.

For initial success, I would advise you to connect to a CAN in the comfort area, since in my experience all manufacturers still primarily see open communication directly in CAN messages: press a button and a cyclical message changes on one or two Make the value.

With everything that concerns the drive and driver assistance systems, if that is still connected via CAN, you can actually only read data openly. For all the control commands you have to go into higher protocols, with the latest vehicle generations there's also the topic of encryption, but then these segments are connected via Ethernet or Flexray anyway and you won't get very far with a simple electrical tap.

In the multimedia sector, a higher protocol is often superimposed on the simple CAN message in order to display more complex contents that comprise more than 8 or 64 (CAN-FD) bytes. That becomes very individual, depending on the vehicle manufacturer.

All right, then I'll deal with the radio control and the speedometer today.
Let's see what is possible.