27" iMac hard drive fan running wild!!

I recently updated my 27" iMac 11.1 Intel i5 to 10.6.3 and also installed the two new firmware updates that Apple has issued. My internal fans begun operating continuously at virtually full speed (5,000 >5,300 RPM) according to iStat Menu Pro. There are three separate fans and the one that is going ballistic is the one for the hard drive even though the temperature seems reasonable (38>40c). I've done some research on the Apple communities and there seem to be quite a few folks with this problem.


I've tried several of the suggested solutions including re-installation of the firmware. My System profile is showing it installed correctly.

SMC Version (system): 1.54f36

I also have repeatedly reset my power management by unplugging the power chord and pressing the start up button for 5 seconds and then restating. The fan turns on immediately even from
cold and ramps up to maximum speed within 10 minutes. Besides the wear and tear on the fan part, the noise reminds me of the old G4 Quicksilver Macs that sounded like a 747 warming up inside my office. Very distracting.

I next ran the Apple Hardware Test off the installation disks and it found a problem. The code is:

4SNS/1/40000000:TH00-9.00

After I got this result from running the regular hardware test, the utility advised me to unplug everything from the iMac and run the Extended Test. This took almost 90 minutes and the same problem code came up.

Can anyone help with this? I am in a very remote area quite far from an Apple Service Center and it will be a big hassle to get it to them, but the noise of the fans is very distracting and annoying. Should I hang loose until 10.6.4 or is the Apple Hardware Test analysis of 4SNS/1/40000000:TH00-9.00 indicative of something that must be repaired?

Thanks very much for any and all suggestions/advice

Kitemandu