Well, this thread is like one of those american series that, after 3 seasons gets cancelled. The cliff-hanger never gets resolved! 
Old thread ressurection.
As has already been said before.modern vehicles have a twisted pair of wires that carry info from one ECU to another, usually known as the can bus with variations.
Electrical faults can be very problematic to find, reading and clearing the codes with diagnostics of the first port of call as some may well be historic codes. Then see what codes come back. Usually U codes indicate communication issues.
But as the signals are all sent over the twisted pair then de-multiplexed almost anything wrong anywhere in the electrical system can cause all sorts of things to go haywire. Sometimes even as simple as a dodgy earth to a goosed ECU or damaged harness.
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