Fan sporadically maxed on wake-up due to unavailable sensor temperature

[Daniel T.]

I'm running Kubuntu on my Lenovo ThinkPad X1 Carbon (4th generation). Since a recent upgrade to 20.04 LTS, I have the following problem.

Upon wake-up from standby the laptop's fan is sporadically set on max speed (around 7000 RPM) regardless of the actual CPU load. It helps to put the laptop to sleep and wake it up again. Then there is a chance the fan will react normally to CPU load and temperature.

Running sensors when the fan is maxed, I get the following:

---
$ sensors
iwlwifi_1-virtual-0
Adapter: Virtual device
temp1: +35.0°C

pch_skylake-virtual-0
Adapter: Virtual device
temp1: +42.5°C

BAT0-acpi-0
Adapter: ACPI interface
in0: 16.97 V

thinkpad-isa-0000
Adapter: ISA adapter
fan1: 6932 RPM
temp1: N/A
temp2: N/A
temp3: +0.0°C
temp4: +0.0°C
temp5: +0.0°C
temp6: +0.0°C
temp7: +0.0°C
temp8: +0.0°C
temp9: +0.0°C
temp10: +1.0°C
temp11: +0.0°C
temp12: +0.0°C
temp13: +0.0°C
temp14: +0.0°C
temp15: +0.0°C
temp16: +0.0°C

coretemp-isa-0000
Adapter: ISA adapter
Package id 0: +43.0°C (high = +100.0°C, crit = +100.0°C)
Core 0: +42.0°C (high = +100.0°C, crit = +100.0°C)
Core 1: +43.0°C (high = +100.0°C, crit = +100.0°C)

acpitz-acpi-0
Adapter: ACPI interface
temp1: +48.0°C (crit = +128.0°C)
---

And running it when the fan behaves normally, i.e. in accordance with the CPU load, I notice that temp1 is no longer N/A but has a value.

...
thinkpad-isa-0000
Adapter: ISA adapter
fan1: 3240 RPM
temp1: +46.0°C
temp2: N/A
...

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: acpi (not installed)
ProcVersionSignature: Ubuntu 5.4.0-37.41-generic 5.4.41
Uname: Linux 5.4.0-37-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.2
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: KDE
Date: Tue Jun 16 09:17:14 2020
InstallationDate: Installed on 2019-11-22 (206 days ago)
InstallationMedia: Kubuntu 19.10 "Eoan Ermine" - Release amd64 (20191017)
SourcePackage: acpi
UpgradeStatus: Upgraded to focal on 2020-05-09 (37 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.