[SOLVED] Intel CPU fan stopped working after update

[Ethem]

I installed an update from the update manager relating to Intel CPU microcode/firmware about two or three hours ago, and then shut down my computer. Now when I boot it up I get a "CPU Fan Error."

What should I do? I'm using a separate computer to post this thread.

Here's my system specs from February (I haven't changed my hardware since then, except installing nvidia-driver-390 that same month s which has worked fine):

System:
Kernel: 5.4.0-65-generic x86_64 bits: 64 compiler: gcc v: 9.3.0
Desktop: Xfce 4.14.2 tk: Gtk 3.24.13 info: xfce4-panel wm: xfwm4
dm: LightDM 1.30.0 Distro: Linux Mint 20.1 Ulyssa base: Ubuntu 20.04 focal
Machine:
Type: Desktop Mobo: ASUSTeK model: P8Z68-V LX v: Rev X.0x serial: <filter>
BIOS: American Megatrends v: 0401 date: 07/15/2011
CPU:
Topology: Quad Core model: Intel Core i5-2500K bits: 64 type: MCP
arch: Sandy Bridge rev: 7 L2 cache: 6144 KiB
flags: avx lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx bogomips: 26487
Speed: 1606 MHz min/max: 1600/3700 MHz Core speeds (MHz): 1: 1605 2: 1605
3: 1606 4: 1605
Graphics:
Device-1: NVIDIA GF116 [GeForce GTX 550 Ti] vendor: eVga.com.
driver: nouveau v: kernel bus ID: 01:00.0 chip ID: 10de:1244
Display: x11 server: X.Org 1.20.9 driver: modesetting unloaded: fbdev,vesa
resolution: 1920x1080~60Hz
OpenGL: renderer: NVCF v: 4.3 Mesa 20.2.6 direct render: Yes
Drives:
Local Storage: total: 931.51 GiB used: 561.49 GiB (60.3%)
Partition:
ID-1: / size: 915.40 GiB used: 561.49 GiB (61.3%) fs: ext4 dev: /dev/sda5
Sensors:
System Temperatures: cpu: 39.0 C mobo: N/A gpu: nouveau temp: 43 C
Fan Speeds (RPM): N/A gpu: nouveau fan: 1260
Repos:
No active apt repos in: /etc/apt/sources.list
Active apt repos in: /etc/apt/sources.list.d/official-package-repositories.list
1: deb http://packages.linuxmint.com ulyssa main upstream import backport
2: deb http://archive.ubuntu.com/ubuntu focal main restricted universe multiverse
3: deb http://archive.ubuntu.com/ubuntu focal-updates main restricted universe multiverse
4: deb http://archive.ubuntu.com/ubuntu focal-backports main restricted universe multiverse
5: deb http://security.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse
6: deb http://archive.canonical.com/ubuntu/ focal partner

[gittiest personITW]

Judging by your CPU temps, your fan is fine.
More likely is the sensor has stopped working.
Either you can wait for a new update or make a Timeshift restore point and try 5.8 kernel.

[Ethem]

Either you can wait for a new update or make a Timeshift restore point and try 5.8 kernel.

How would I go about doing the latter? I presumably can't do much on my PC if the CPU has no working fan...

[gittiest personITW]

If your fan wasn't working, the chances are you wouldn't be able to get as far as booting, opening your browser, posting a message with your cpu at 39 Celsius.

[Ethem]

If your fan wasn't working, the chances are you wouldn't be able to get as far as booting, opening your browser, posting a message with your cpu at 39 Celsius.

As I wrote in my first post, "I'm using a separate computer to post this thread." The stats I posted are from February.

[gittiest personITW]

EDIT....

Boot into Live Mint and do a system restore through Timeshift.

If your fan isn't working from boot to GRUB then it is a hardware issue rather than a MINT issue. Check your connections are plugged in properly.

[Ethem]

EDIT....

Boot into Live Mint and do a system restore through Timeshift.

Just to make sure, I'd create a USB (like I did to install Linux Mint in the first place), insert it, start up the computer, and then I'd use the BIOS to boot into it and it'd allow me to use Timeshift?

[gittiest personITW]

Yep

[Ethem]

Looks like the problem was far more mundane. The fan was so dirty (I've had it for almost a decade) that... the fan wasn't starting, even the moment I turned the computer on.

So I cleaned it and it works. That was anti-climatic. The Intel CPU microcode update had been a coincidence. Will add "[SOLVED]" to my thread title accordingly.