I went back to Device Manager. The yellow triangle was gone. had moved to "System devices" and was now named Sony Firmware Extension Parser .
Then, deep in a 2012 VAIO support thread (archived, in Italian), I found a real clue: "SNY5001 is the Sony Firmware Extension Parser. Without it, Windows can't talk to the EC (Embedded Controller) for fan curves and battery health." acpi\sny5001 driver
That's when it clicked. The fan wasn't broken. Windows simply didn't know how to control it because the driver was missing. The laptop was running a "safe mode" fan profile: ON all the time. I went back to Device Manager
I installed it. It took 10 seconds. No reboot needed. Then, deep in a 2012 VAIO support thread
A few years ago, I bought a used Sony VAIO laptop. It was a beautiful machine—sleek, magnesium-alloy body, a gorgeous 1080p screen. But within an hour of using it, I noticed a problem: the fan was always on. Not loud, just a constant, low whirrrrr that never stopped, even when the CPU was at 2% usage.