The K40 is an excellent place to start. If the OP's car hasn't had it changed then I would try that and see if it changes the computer's status. That little relay center controls the power to everything including the computer. It's only about $100 and takes 5 minutes to replace...might just solve the problem he's having.

Remember, even honest mechanics make (costly) mistakes. They will never admit the computer was not the problem after they replace it and discover it doesn't fix it. They will then find something else to blame. As others have said failures of the main computer are very rare...not that it is impossible, but the frequency of failures of the K40 is like 10000X that of the CPU so I would play those odds any day and replace it and see what happens.

__________________
Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz