I know it is a stretch, but I have been in a business along time dealing with cheap Asian parts which is what the XYZ printers are made off. Trust me, I had a 1.0 that I stripped every trace of XYZ from. But my point is that maybe, the fan is bad. They do die some times and the rate is much higher with Chinese fans which again is what is in this printer. The fan is not on any kind of control in fact i would be willing to bet that if it is connected to the mainboard it is simply connected to the power buss and nothing more. When the machine is on the fan is on. It's that simple. If it is connected to a control line then that would be the second flaw of Chinese stuff. Over complication which also aids in failure. That fan simply needs to run when power is on and nothing more. If that is the case then the logic that controls it has failed. That would mean either the MOSFET that switches ground has failed or the Processor itself has failed and the control line from it to the MOSFET is no longer functioning meaning the board is hosed. Your only course then would be to wire the fan directly to the power supply.

Again though I suspect the fan is bad. You could test it by taking it out and connecting it to a known good 12 volt supply. Red to Positive and black to ground of course. If it runs then your back to the logic being faulty.

Pretty much everything in your 3d printer is made in china now, regardless the brand. you can take apart the high quality 3d print apart and found almost every part is also made in China. The only difference if whether they pass strict quality control, and that is company dependent.

Again though I suspect the fan is bad. You could test it by taking it out and connecting it to a known good 12 volt supply. Red to Positive and black to ground of course. If it runs then your back to the logic being faulty.