This is a clear and 100% effective solution for all iMacs with 4SNS/1/40000000:TH00-9.000 problem after replacing a HDD: https://www.elvikom.pl/imac-21-5-27-blad...
Please note that Macs Fan Control DOESN'T solve the problem because you still have an error in Apple Hardware Test! Macs Fan Control does only control fan speeds and has nothing to do with a HDD temperature sensor detection.
My solution resolves all the issues after HDD replacing, like:
- Mac OS runs very slow,
- fans are running at the maximum speed,
- kernel task is equal or above 100% in Activity Monitor,
- AHT and ASD are reporting TH00 temperature sensor error.