And finally, this whole "proprietary systems" junk is nonsense. In North America at least, all modern vehicles conform to an open specification called OBD-II
OBD-II is a protocol. The software that the PCM (as well as any peripheral computers) is completely proprietary - if there's a firmware bug, you get to pay the dealership $150 a pop to update it. And even with OBD-II, you just get a code - you still have to find the dead tree somewhere that translates that code into information you can use to fix the problem.