One of the most common misconceptions people have about their cars is that automotive computer systems are complex. On the contrary, automotive computers are some of the simplest and most straightforward computers you will ever interact with. Unfortunately, manufacturers like to profit of any aspect of the vehicle they can, and one of the most offensive ways to do this is to make the computer very complex to interact with.
You can read about the history of on-board diagnostics here, but I'll sum up my opinion on it. Various governments have seen the value of having a standard interface to certain parts of the car, but they typically only care about enforcing emissions and safety regulations. While both valuable, they have created the perfect framework to also enforce Right to Repair, but no one seems to have figured this out yet.
Interestingly though, manufacturers do need to enable a vast network of their dealerships to work on all aspects of their vehicles, not just the mechanical ones. The only practical way to do that is to create relatively user friendly software and tooling that allows even a mechanic to understand what's going on inside the brain box(es) of the car.
Now comes the problem of profits. On one side, you have the software needed to communicate and repair any part of the electronic systems you can think of. On the other side you have a consumer who paid good money for their vehicle, and now is in need of that software. So what to do? Charge. A lot.
In GM's case, a copy of Techline Connect (software that rolls all the tools you'd need for your car into one) you'd have to fork over $4,328 for exactly one year of use. Oh and by the way, you'll need a ~$1,000 interface to connect your computer to the car.
Pardon my swear words but fuck that. I'll acquire it some other way.
Acquiring the Software
I am not the first person with this issue, and Chinese manufacturers of knock-off vehicle interfaces are champing at the bit to help. Interfaces like this one will run you about $150, and if you scroll down to the bottom of the description you'll find that they come with GDS2 and Tech2Win, 2 of the major components of GM's Techline Connect. Awesome! Certainly beats almost $5,500 just to get going! Except...
You need to make your own decision about this, but that software is pirated. I have no idea how exactly they get away with it, but that software is not intended to be distributed that way, and you do have to do some strange things during the installation of the software that lead me to believe it is likely virus-laden. Cargo from the bay is often suspicious.
But I Don't Care!
Frankly, I don't give a crap that GM doesn't get their megabucks out of me. We're working on a truck from 2001 and I'm not a mechanic. Maybe if I were making money fixing peoples trucks, I'd feel differently. As a regular consumer, just trying to fix my own junk, I won't lose sleep about GM's bottom line. GM had the opportunity of getting as much as twice the price of that knock-off out of me if they made some sort of official route, but I have no such option.