Some manufacturers are more willing to share this software than others. I don't really know when exactly we're crossing the line where it becomes deliberate DRM instead of just poorly available proprietary software. The end result is the same.
Another interesting situation is when you lose all of your car keys. Usually it's easy for your authorized repair shop to fix this, although they might need to have the manufacturer do it remotely(!). For independent shops it's not necessarily as easy as just plugging in a laptop, often they'll have to actually physically replace parts of the car in order to pair their new keys.
Of course, there's a huge market for reverse engineering all this stuff so the indie shops continue to thrive despite many repairs now requiring extensive software reverse engineering.
I don't drive a car but people in my family do(second hand Fords so no fancy expensive sport cars), and when they had issues(including replacing core engine stuff or electric stuff) the either bought some after market compatible part or went to the place where they scrap crashed cars and buy original parts from a destroyed car. It would suck if this cars for normal people will get DRMed to hell.