if the dealer says its an 80% chance and you have all the risk. You are in the wrong shop. A dealer/tech needs to stand behind such testing even though getting the odds any better than 80% is probably unrealistic.
Let me try to tell you why. First as I said there is no way to test the controller except as to end function. Just because the final output is wrong doesn't necessarily mean it is software or hardware related.
The way it works in the shop is that a tech using standard procedures and good logic starts to think he has a controller problem. he hypothisizes logical testing and in an hour or so he has the sheet you posted and the 80% answer. Now he could do a couple more hours testing and get the risk factor to 85%, now he could do 4-5 hours more testing (if he is smart enough and has the techniques) and he might achieve 88% risk factor. If you understand that labor has value (by the hour) then the smart tech does the least amount of testing that gives the highest initial risk factor. Then HE (the shop) takes the risk. He wins by charging more time than it takes and having judged the odds correctly. Since there is no amount of testing that assures the absolute answer some amount of this technique has to take place.
If the shop can't live with the level of risk they can establish then they shift the risk to you and the level of testing all of a sudden doesn't matter to the tech/shop.
I really don't know what to tell you if you can't find a shop that takes responsibility for their diagnostics. My main job in my shop with 8 technicians is establishing risk and taking it!! My techs can do so to a point but high dollar controllers always await my deciding when we are going to take the risk. I tell the customer that testing says this and I need that much approval. if I'm wrong we now have a "known good controller" for the next time. If I'm right the customer has spent the least amount necessary to get their problem repaired.
If they think at some point that they wish to use my data from testing to take the risk I bill for the testing and am done. NO warrantee till the job is complete. And no parts paid for that aren't needed!
Bosch Master, ASE Master, L1
33 years MB technician