OK,.. Now I'm about 97% sure it's your alternator. You didn't mention that your battery light was coming on in your other thread.
When my alternator crapped out and shot up to 17 volts, the battery light did come on (but no cell,.. and there is 4 different codes for the alternator)
I went through the FSM but couldn't find the info to say what conditions turn on the "BAT LIGHT" but it may simply be the voltage being too high ???
The voltage regulator is still in the alternator (the big ass diodes and stuff) it's just some extra "control wire" that turns everything up and down is done by the ECU.
Essentially,... your alternator is misbehaving and not doing what it is being told.
I don't recall anyone here on this forum that had to replace the ECU (except to put in the MSP upgrade) but there has been MANY threads about the alternator including the two or three rebuilds being put in before they got one that worked.
PS,.. Two of my alternators "went bad" from being over tightened and the bearing started squealing (before I took over the maintenance).
Glad you pointed that out! Thanks!
A friend of mine actually heard about my issue and decided to buy me a re-manufactured Alternator for my birthday (best gift ever?).
I'll slap it in (and be careful not to over tighten) and see how it rolls! Check back Monday!