After replacing the nozzle (and thermistor) on my P1S, I immediately received errors 0300-8010 2003191 and 0300-0300-0001-0001. One in Bambu Studio, and the other on the printer screen.

In fact, it's the same thing:

The hotend cooling fan speed is too slow or stopped

The hotend cooling fan speed is abnormal

Immediately, we go to the official documentation - https://wiki.bambulab.com/en/x1/troubleshooting/hmscode/0300_0300_0001_0001 We check the connector and everything like that. I removed and reattached it several times. Visually, I found no problems. Nothing works. I think about ordering a new one. But I decided to do a bit more Googling in the context of replacing the nozzle. Something like:

The hotend cooling fan speed is too slow or stopped after nozzle change

And I stumble upon a forum where there are suspiciously many identical situations. Nozzle replacement - the fan doesn't work. And one comment turned out to be the solution to this issue.

From the post, it's clear. You need to reconnect the cooler while the printer is on. Then turn off the printer (when the cooler starts) and turn it back on. I did all these procedures with the printer off. Safety and all that. But this all seems like some strange bug.

So I try:

The cooler works. BambuStudio shows a different error (Toolhead front cover fell off). We attach the Toolhead back. I didn't make a video of the whole process. Out of joy, I only recorded the moment when the cooler started spinning.

Here we immediately see in Bambu Studio (the old message The hotend cooling fan speed is abnormal has disappeared)

We turn off the printer. Turn it on. Start a test print, and everything works. The fan spins - the filament melts. So that's the deal, folks. I don't know if you can get electrocuted or burned by the hot nozzle - but most likely, you can. So be careful and do everything at your own risk. Everyone is responsible for their own actions.