HP Elitebook 665 G11 fan keeps spinning up and down

[sustmi]

I have a problem with HP Elitebook 665 G11 laptop. The fan keeps spinning up and down in approximately 1-3 second intervals when the CPU is idle.

What are the steps to reproduce (vaguely):

1. Turn on the laptop

2. Use some CPU stress test or benchmark (like https://silver.urih.com/) to heat it up a little bit

3. Stop the CPU stress test and let it cool down for a while

Using HWInfo64 8.24 (https://www.hwinfo.com/download/) I found out that whether the fan is spinning or not does not correlate with CPU temperature that much but it is directly related to "TZ.EXTZ" temperature (in Sensors -> ACPI: HP HP EliteBook 665 15 inch G11 Notebook PC). When the fan is spinning up and down, the TZ.EXTZ temperature oscillates between two values: 33.1 °C and 32.1 °C.

When the temperature rises to 33.1 °C the fan spins up and then when it goes down to 32.1 °C the fan stops spinning. This repeats in 1-3 second cycles.

Here is a video https://youtu.be/Ii_R7ToX3wM (using headphones is recommended but be aware of the noise volume).

Note: The fan RPM is measurement seems not to be very accurate. The sampling speed is low and when it shows RPM less than 1000 it is actually not spinning at all.

It is actually pretty distracting and hard to focus on work when the fan keeps spinning up and down in such short cycles.

I think there should be some hysteresis. Based on the tracked temperature changes I would recommend difference at least 3 °C. For example: spin up when the temperature rises to 35 °C or above and stop when it goes to 32 °C or below. Now, there is no hysteresis at all (or maybe 1 °C but since the measurement goes in whole ° C steps it still causes fast cycles when being on the edge between the two values).

I am OK with the fan spinning up and down every now and then but the cycles should be at least few minutes long and not 1 second.

When the CPU is loaded and the device heats up, the fan is spinning continuously as it should.

I believe this has to be fixed with BIOS/EC controller update.

Additional information:

OS: Windows 11 Pro 24H2 (Build 26100.3775), all current system updates installed

BIOS version: W77 Ver. 01.03.01 (from 2024-11-26)

The device is new and the fan is clean.