Thanks for all the information. I'm at 84,000 miles, so unfortunately, it won't be covered under warranty, but at least I know there is a known cause. I also have found that I can stop charging when it is back to 32A and it ramps up to 48A again for a few minutes.
Um. When doing my $DAY_JOB, I troubleshoot $RANDOM electronic hardware for a living. Under, "Guessing madly" sounds like something is overheating: It gets hot, fails, and stays that way. Turn everything off, the fault clears, start it up, then it gets hot again, and dies.
That advice is worth exactly what you paid for it.
There's lots else that could go wrong other than the trannies and stuff in the PCS: Loose wires, corrosion, who knows?
But there's another possible point. Say that you've been charging using a Mobile Connector all this time, or using lots of public AC chargers, like Charge Point. The first of those won't charge at a higher rate than 32A; lots of the second ones never charge faster than 32A. So, if you just put in a brand spanking-new Gen 3 charger, put it on a 60A breaker so you can get the whole 48A, it Just Might Be that that PCS module has been dead for a while, and
now you're finding out.
Dunno. don't know what kinds of logs the car has. But there's the possibility that this PCS has been dead for a very long time. Long enough, possibly, to have been around when the car was still under warranty.
You're not going to get any true-blue joy out of Tesla on this one. But if you're nice to them and give the the hang-dog look, well, from time to time I've seen them take something off the bill.
A little searching around these forums reveals that, for one person, a PCS replacement ran $2000. But that (a) might be an actual dead PCS, which you may or may not have and (b) time moveth on, prices of things drop, so you Never Know; repair costs for this item may have dropped.
Finally: It's not common, but there are third-party Tesla repair people, and
sometimes they're cheaper. Again, dunno, and depends upon where you live.