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HP Zbook 15 G3 thermal/fan issue

I have a HP Zbook 15 G3 that runs the fans at full speed almost constantly. I have tried cleaning the fans and entire laptop by disassembling, I replace then fans and thermal cooler (heat pipes, heatsinks, thermal paste ), changing the power profile in Windows 10, monitoring the system board under a thermal camera (no excessively hot components) and upgrading and downgrading the BIOS. The issue is the same if running on battery while plugged in, or running without the battery while plugged in, or without being plugged in with only battery. I also tried removing all non-vital components (WAN module, GPU, switching SSDs, etc..). This issue is the same if I run Windows or Ubuntu. I can see that one of the temperature sensors is reporting an abnormally high temperature of 100C all the time, but nothing on the board is that hot. The CPU is also running at 0.79GHz which can be resolved by using Throttlestop and disabling the PROC_HOT (and is stable for hours while this is disabled).  


The wired thing is, when I unplug one fan (either GPU side of CPU side) the other fan spins downs for a while (30 seconds or so) before spinning back up to compensate for the loss of airflow/cooling. This is the second HP laptop I have worked on to have the same issue (although I don't remember the model of the first). Both of the laptops were out in the field, and I have the suspicion that they were left in a cold vehicle overnight.   


I cannot tell which APCI thermal sensor is reporting the incorrect value, and don't know exactly what kind of thermal sensors are used on the board (IC, thermal diode, thermal resister) or where they are located. Has anyone else ran into this issue and been able to find the solution?

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I found a solution (crossing my fingers it's a permanent one)


First off, I realized my BIOS and other drivers were already up to date. So no chance of that fixing the loud fan. I mean, the fan sounds like it's of poor quality to be frank the way it rattles. I'm more than sure HP could have put a better, smoother, quieter fan in the machine.


The most critical thing is to control the fan! There are a variety of tools out there for this, but I found this Notebook Fan Control (nbfc) one to be very convenient: https://github.com/hirschmann/nbfc/releases

When you open it, you'll want to choose a profile and there is already one for the Zbook conveniently enough. Seemed to be fine for me. Click the radio button "Enabled" and it should IMMEDIATELY cut the fan and the noise.


You can still hear the fan when it spins, but it's no where near as loud. I imagine it's either a different fan spinning or it's not running at the same speed. This tool will show you how fast the fan is running too (in % not RPMs or anything). 




The other reading this tool provides is the CPU temp and it's in your tray too. Very nice. It's cool - this machine is not running that hot. So there is NO REASON for the fan to be running the way it is. The machine is more than fine on passive cooling. So I assume this is all mostly a software problem...But I do think that even at 100% or even 50% speed, the fan is way too loud. I really do think they could've put a better fan in there...But at least now I don't want to throw this computer off a bridge.


Also, I noticed when you change the fan speed manually using this utility that you can hear the fan start spinning and even at 95% speed it doesn't make as much noise. There's no rattling. This little utility is like magic for that horrible fan noise.

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