Looks like Harness is suspect ..

BUT...............

Take the old OVP out and see if it is the original..there was a part# change
[ ARCHIEVES has that info] and if so, change it regardless..
Then charge the battery right up to full state and retry the car..

If still persist..Wire harness is just about had it...that is the most likely, but your complaints do fit OVP/Low Voltage ...so I would do that first.

I am assuming you did not go and get a code with your tool from Pin #4 as you state, but rather, you used the Factory DM SW/LED that is there ..correct?

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A Dalton