You were absolutely right. Today I experienced the same problem. The “Sensor 3 error” was just a red herring since the factory fan setting does not read that temperature, only local_f75303@4d and cpu_f75303@4d are being read. Although you can use cpu@4c to control the fan using ectool thermalset command but that’s another topic.
Not only the “Sensor 3 error” persists, the
--sensor name -------- temperature -------- ratio (fan_off and fan_max) --
local_f75303@4d 308 K (= 35 C) 0% (313 K and 343 K)
cpu_f75303@4d 308 K (= 35 C) 0% (319 K and 327 K)
ddr_f75303@4d 309 K (= 36 C) N/A (fan_off=401 K, fan_max=401 K)
Sensor 3 error
local_f75303@4d and cpu_f75303@4d failed to update and stuck at these temperatures.
sensors gave weirder results:
Adapter: ISA adapter
fan1: 0 RPM
local_f75303@4d: +34.9°C
cpu_f75303@4d: +34.9°C
ddr_f75303@4d: +35.9°C
cpu@4c: FAULT
and
acpitz-acpi-0
Adapter: ACPI interface
temp1: +34.8°C
temp2: +34.8°C
temp3: +35.8°C
temp4: +180.8°C
As such, the fan won’t spin. If I stress the CPU it’ll go 100C and power throttled down to as low as 12W without using the fan. The only way to cool down is to use ectool fanduty to speed up the fan manually.