Jumping into this thread to say that I've had very similar symptoms (couldn't check error codes because I lost my OBD scanner), except I've never heard the fans come on, ever.
I considered DIY-ing it (
[DIY] IPU fan Code P1643 and P1448) but decided against it because I technically can't confirm if it's actually a P1448 and/or P1634 code.
Brought it into the dealership and they're quoting me $1500 for both the MCM module and labor, they're saying that one of the previous owners (I'm the 3rd owner) installed some janky extra wires in there and so the 15/150 warranty doesn't cover it (I'm in the Northeast).
By any chance, does anyone know how much the MCM module would cost and/or where to get it, and how easy it would be for me to fix it?