From ArchWiki

This page describes additional steps and other hints for the ASUS X470 PRIME mainboard.

UEFI Temperature Sensors

Warning: This board uses the ITE IT8665E super I/O chip, which is buggy and can lead to fans stopping or spinning at 100% (ASUS cannot or won't fix the BIOS)

See lm_sensors#Installation and Lm_sensors#Asus_B450/X399/X470/A320M-K/A320M-K-BR_motherboards_with_AM4_Socket if needed, then install asus-wmi-sensors-dkms-gitAUR.

Load the module afterwards:

# modprobe asus_wmi_sensors
$ lsmod | grep wmi_sens
 asus_wmi_sensors       20480  0
 wmi                    36864  4 asus_wmi_sensors,asus_wmi,wmi_bmof,mxm_wmi

Check if it's working:

$ sensors
 Adapter: ISA adapter
 CPU Core Voltage:          1.31 V  
 +12V Voltage:             11.97 V  
 +5V Voltage:               4.99 V  
 3VSB Voltage:              3.29 V  
 CPU Fan:                 1194 RPM
 Chassis Fan 1:            618 RPM
 Chassis Fan 2:            838 RPM
 Chassis Fan 3:            832 RPM
 AIO Pump:                   0 RPM
 Water Pump:                 0 RPM
 CPU OPT:                    0 RPM
 CPU Temperature:          +72.0°C  
 Motherboard Temperature:  +36.0°C  
 Chipset Temperature:       +0.0°C  
 Tsensor 1 Temperature:     +0.0°C  

Depending on BIOS version, some temperatures are missing (Chipset works with 5202).

Reading out those sensors too often or in quick succession can make the fans stop randomly or run them at 100%.

Other modules like it87 can sometimes read out, but the chance of fan failure is much lower with asus-wmi-sensors-dkms-gitAUR.

Max CPU temperature 75 °C or cpu fans at 100%

In the Prime X470 UEFI, CPU alarm temperature threshold can't be higher than 75 °C (which is much, much too low for Ryzen), and lets your CPU fan spin at 100% when crossing that threshold. You can cap the CPU at 74°C in the UEFI, eliminating the fan issue, but limiting the power of the cpu slightly as well (go benchmark).

It's also possible to bind the chassis fans to the "Motherboard Temperature", which can be an acceptable workaround for this issue.