Fan Issue/Failed HD - 4SNA/1/40000000:TH00-9.000 Error - Need Help on Next Steps

I have an iMac (27-inch, Mid 2011), and the internal secondary hard drive failed. I have the primary drive which is a 250 GB SSD which is working fine, but I had secondary files and all back-ups on the failed drive (files are in iCloud so no issue - just mainly lost the backups). Since the drive when out, I tried the Drive Utility and ran First Aid, but nothing happened (it said done in about 1 nanosecond).

I ran Apple Diagnostics and got this error - 4SNA/1/40000000:TH00-9.000

Anyway, as I operate the iMac, the fan starts normal but then goes full tilt. I researched and found that that error is a thermal temperature issue.

Question - can I just remove that failed HD and would the issue likely go away? I can live without the secondary drive, and just plug in an external for backups. The fan issue didn't start UNTIL the HD failed. Or should I replace the thermal sensor? And if I have to replace the thermal, does it require another HD so that I should replace new HD to replace the failed one?

While I never opened the iMac other that to add more memory, I am proficient having built many PC's over the years - and did watch a youTube on how to replace a drive.

Other than the failed internal backup drive, the unit works fine (other than the noisy fan). I can manage fine with the 250GB as I have most everything in the cloud.

Thanks in advance.

iMac 27", macOS 10.13

Posted on Jul 19, 2019 11:45 AM

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Pezmeister Author

Level 1

10 points

Posted on Jul 20, 2019 7:33 AM

Allan - no your suggestion was helpful.

I did type in the wrong error - you are correct, it is 4SNS

And yes, I purchased directly from Apple and added the secondary hard drive at purchase.

I've copied your answer below as I believe you deleted it, if anyone else has ideas.

Wondering about this:

While I never opened the iMac other that to add more memory...

Did you buy the computer with the second drive already installed? That model never shipped from Apple with two internal drives as far as my research has found. There are however aftermarket kits to allow replacing the optical drive with another HD or SSD.

Are you sure the code starts with "4SNA" and not "4SNS"? I don't have a code SNA for High Sierra.

If it is"SNS," then that code translates to a failed temperature sensor servicing the hard drive, NOT the hard drive. That would explain the high fan speeds. Codes for hard drive issues start with "4HDD."

On many iMac models you must add a special cable to maintain sensor function and quash spurious readings if you change the main hard drive. Example:

https://eshop.macsales.com/item/OWC/DIDIMACHDD11/

That said, have you done a SMC reset? That can help fan issues and is easy, so try it first:

How to reset the System Management Controller (SMC) on your Mac - Apple Support

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