4SNS/1/40000000:TH00-9.000

It is a sensor for the Hard Disk Drive. Please make an appointment at the Apple Retail Store - Genius Bar and take it in for service. If you are not in the USA or cannot set up an appointment this way, then contact your local Apple Store directly.

You cannot repair this problem. I believe this is the HDD's temperature sensor.

if you are running ANY anti-virus uninstall it as the developer describes on their web page,

if you are running any Mac Keeper, Cleaner, etc, uninstall it, Any 3rd party network tools uninstall them now.

These applications do nothing but cause problems.

If your computer is in direct sunlight, remove it.

if your computer is near a space heater, remove the space heater.

if your computer is near pets remove the pets and spray compressed air in the vents and be careful not to damage the computer.

What do these have to do with a bad sensor? 😕

a bad sensor was your assessment, not mine. Mine was the fan.

Did I suggest something that would potentially damage the users computer or cause a larger problem? if not why are you asking me about what this has to do with a sensor?

4SNS/1/40000000:TH00-9.000

Yes Temperature sensor for the Harddrive.

You will have to take it in for a 'Apple Service Diagnostics' test.

Genius reservation http://www.apple.com/retail/geniusbar/

on-line https://getsupport.apple.com/GetproductgroupList.action

check warranty https://selfsolve.apple.com/agreementWarrantyDynamic.do