I've searched, found promising statements and a bunch of conflicting statements.

What should the voltage read at idle no lights/ac/stereo? I'm seeing 13.3v-13.6v
What should the voltage read idle with load such as ac/stereo/lights? I'm seeing 12.2v-12.6v
after driving a length of time 5-15min, then sitting idle I'm seeing voltage 11v-11.8v with load sometimes dipping in the high 10's.
after driving a length of time 5-15min, then sitting idle for 5-10minutes I'm seeing 12.2v

While driving stopping and turning with the fan on 2 and ac on I'm seeing voltage always dipping to 11.8-12.1v

After driving for about 5-10 minutes I'm seeing the EP light on gear selector (stronic), Tire pressure, check engine and we are seeing the following codes.

p1747
p0700
p1613
p1611


Switched out TCM and had the battery checked.

 

I'd hazard to guess the alternator is going out. If a new battery didn't fix the problem.

 

12.9 is the break even point. Below that you are not charging, but discharging. Normal loads from light and such should not affect the charge voltage at all.

This assumes you are measuring the actual battery terminal voltage. If you are looking at the volts reported by the ecu that might be different.

 

Gotta wire my gauge in still, I was going to tap into the constant for the stereo. That's what I've always used in previous vehicles, I assume that will be fine in the Mini

 

I checked across the terminals this morning reading seems fine 14v and 12.9v max fan,ac,lights,stereo. Other reading were through the ecu. Still seeing all these codes replaced the parts checked wiring. Clear and they come back within an hour of moving

 

I'm not sure where any of them are as I've only been involved with Mini for about a month, but that sounds like a grounding issue to me. Need to find all the ecu grounds and clean them real good.

 

I know this is like 2 years late. I've been holding on to this car because it bothered really bad that it broke so sudden.


I fixed all these codes

p1747
p0700
p1613
p1611


By replacing the Tachometer above the steering column.

I noticed this thing started acting up (going off/on) a few months later. It made me wonder if this was the root cause and was just not showing symptoms at first.
I replaced this with one off ebay for $25 bucks a few weeks back. So far she is still up and running.

No more codes, no more EP, no more transmission not shifting.