A hard drive sensor or logicboard error.
Backup your personal data off the computer onto a external drive and disconnect.
Download the free OnyX here and run ALL the cleaning and maintainence, as well as the intital checks, then reboot at the end, hopefully it will be fine.
Your computer will perform a bit more snappy and if there are no SMART or other warnings from OnyX then your drive is fine.
Download the SMC fan control and iStat, take a note of your fan speeds, if they are running fine and your machine is cool, then I wouldn't worry about it.
A hard drive failed sensor is no major thing in my opinion, as long as your fans are working and keeping hte machine cool, so will the hard drive be cool.
Of course if your under AppleCare or warranty there's a excuse to get your machine taken care of for free, but it might not come back as expected, so get your data off while you have a chance and DIsk Utility >Erase free space for privacy.
I found that my Macbook Pro (Mod. MB166xx/A) had a call by Apple to a replace your logic board for free. Finally, I replace it but I had to paid an extra litte fee (compared to buy a new logic board) because I did out time.
I hope this can help you.
Here you can check your model: http://support.apple.com/kb/HT4132
error code 4SNS/1/40000000:Th2H-60.250
System sensor Th2H-60.250 temperature sensor on the heatsink.
faulty sensor on the logic board, the board has to be replaced.
take in for repair:
Genius reservation http://www.apple.com/retail/geniusbar/
check warranty https://selfsolve.apple.com/agreementWarrantyDynamic.do