Sensor Error After Hard Disk Replacement

"4SNS/ 1 / 40000000: T H 00 - 9.000

4SNS - System sensor

T - Temperature

H - Hard disk

As you can see yes the sensor within the HD is not active.

Did you replace the HD with a SSD or a HD? If not your system should still be covered under extended warranty. You'll need to talk with Apple.

If you swapped out your drive then the drive you put in does not comply with the newest SMART spec."

Get Macs Fan Control, it can be configured to use other thermal sensors to spin down the HD fan

"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."

"I got this same error but did not replace the HD.

Mac won't start. It began showing the flashing folder with a question mark. I looked this up, pressed ""R"" to do a reset. It started and failed to do the reset. I tried again and again and still showed the folder.

It did respond when I pressed ""D"" to do a test. Hence this exact error. Would this mean the HD would have to be replaced?"