Wheel sensor will give you an instant trifecta error not trans failsafe.

A voltage dip can cause many systems to error so when you get any random failsafe they go-to test is alternator.

Get Realtime voltage on the dash with the hidden menu and drive around, the voltage should be about 13.6 +/- 0.3. If you see below 13 for even a millisecond the alternator system is faulty (can be the alternator, a cable (POS or ground) or the voltage regulator. ( Or an 1di0t error (operator error; I forgot to tighten my B+ nut on my alternator when I reinstalled it).

That's the first test and most likely cause. If you have ever gotten random and/DSC/yellow brake as well then it's almost a guarantee that it's the alternator.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)