While it didn't spit out a part number, I had a free program for my Audi that ran on my laptop that was *very* detailed in how it diagnosed, fuel maps and timing, shift points, etc, right down to the voltage to, and resistance of, the little flapper motors in the AC ducts. The full diagnostics was a thing to behold, with lights flashing, engine revving, flappers flapping, windows going up and down...
VAG-COM/VCDS cannot be so inclusive as to know the part number of a failed part. In fact the program does not know that a part has failed. It only knows that a part is not meeting parameters as reported by the control module. The reasons the parameters may not be met are many and are beyond the testing ability of the modules in the vehicle. The module is not designed to ascertain whether or not the part itself has failed.
Too many think the control modules know all. They don't.
As I suggested in an earlier post, tractor owners should push for fault codes to be displayed on the instrument cluster and for a reference document/app to be supplied to help resolve a problem literally "in the field."
Having to buy a diagnostic tool for a one control module machine - the engine - seems onerous to me. Better to have the fault codes in a display on the instrument cluster so a repair can be initiated.
For the more complicated Ag machines with lots of computer control, perhaps a full diagnostic tool will be needed.
Anyone remember blink codes in the early days of auto diagnostics? Simple was good... but it was not very comprehensive. I'm not suggesting the OEMs go to blink codes!
I am suggesting that the OEMs build a means for users to see and begin a process of troubleshooting from the seat of the machine. I really doubt that adds a huge amount of cost. They could supply a module in the machine that communicates to all other modules and queries them for the faults they see. It then sends those messages to the instrument cluster on command. The user of the tractor now has the information they need to decide, can I fix this or do I need the dealer tech. The instrument cluster would have an intelligent display section. Costs would be for the diagnostic module and the enhanced instrument cluster. On a $70k tractor - likely a $2-3k price increase.. not very hugely significant. On a $20k tractor, this scheme would be significant in cost but would also likely be overkill and not necessary. Design trade-offs would be required.
Let's consider an aftermarket solution. It is not going to be easy. With no standards, who is going to be willing to reverse engineer all the manufacturer's control and communication schemes to make a tool? And if you can't focus on all OEMs then how will the research and development costs be spread over a large enough pool to make a tool inexpensive - under $500? Some have asked us to consider this and taking on this endeavor. We're thinking about it but as yet do not see how we recoup our investment.
As one who is in that business for automotive and works for the company that makes an aftermarket VAG tool, I can state that the information needed is not just sitting there for one to draw upon. It has to be mined - literally byte by byte. We have full time staff whose sole purpose is to research what VAG is doing in the controls of their cars. Likewise, to make an aftermarket Tractor-COM, one would have to learn all the communications methods of each OEM. The FTC will not force them to share that information freely. It would take away their competitive edge.
The Right to Repair action is a good start. Let's see where it leads.