pallec
+1y
Somewhere, probably in the airduct, there is a set of power resistors that attenuates the 12 VDC voltage depending on your fan speed.
One, or more, of these resistors are burned. The resistors can have form of 2 or 3 coils.
It is normally located in the intake airduct, so that the resistors are cooled down by the cold intake air. Try to locate the intake air tube, and look for some wires that connects to some kind of small box on the tube.