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Proprietary cable can put the brakes on upgrading Late ’09 iMacs.

Monday, November 2nd, 2009 | Author:

STOP-hard-driveSometimes even the best educated guesses can be thrown for a loop when an unforeseen “X-Factor” comes into play. Such is the case with the Late 2009 iMacs.

As we were getting information together for the new iMac instructional videos, we came across a little tidbit that, apparently, hasn’t been covered anywhere else: Apple has switched the iMac’s method of hard drive temperature sensing. They’ve gone from an external sensor that attached to the outside surface of the drive to a connector that seems to use the drive’s internal sensors.

On first blush, this would appear to be a good thing; an internal sensor is closer to the drive’s mechanics and is likely to be more accurate regarding drive state. Unfortunately, there are no industry standards regarding the ports/pins used to access this information, and each hard drive manufacturer seems to do it their own way. And more unfortunately, when the iMac gets no sensor information via that cable, the heat exhaust fans kick into permanent high gear, so that cable must be connected.

That means, in order to upgrade the internal drive, you need to have a connector cable that’s compatible with the brand of drive that you’re installing… and that’s an Apple service part not generally available to the end user. Pretty sneaky, Apple!

Fortunately, you can reuse the cable that came with your iMac as long as you replace the drive with another model from the same manufacturer we have confirmed works properly with this thermal sensor cable. To determine what brand hard drive your iMac has, go to About This Mac, click on Serial-ATA, and then look for the drive model installed at the factory. If the model has the preface WD, that’s a Western Digital hard drive and if your drive has a ST, that’s a Seagate hard drive. Once you know what drive came with your Mac, you can upgrade to a larger drive and continue to use the thermal sensor…thus avoiding the “ear pleasing” whoosh of fans on high.

Here’s a list of the drives that install into WD factory equipped iMacs.

For the Seagate equipped models, these drives from us will plug right into the thermal cable

Fortunately, upgrading memory is still easy to do, and will show a more immediate improvement in performance than will a hard drive upgrade. That doesn’t mean, though, that somewhere down the road you won’t want to upgrade your hard drive to something larger and/or faster.

We’re all about giving you the most options for upgrading your Mac and that’s why OWC is looking into potential ways to turn this curveball from Apple into a Home Run for you. As soon as we can find a viable method for connecting a different brand hard drive than the one that came with  your 2009 iMac,  you can be sure you’ll hear it first right here on the OWC Blog.

In the meantime, if you get stuck for storage, you can always take advantage of that lone FireWire 800 port (or, if necessary, one of those USB 2.0 ports) and add a fast external storage device, such as the Mercury Elite-AL Pro. The benefit of this is that when you are able to upgrade that internal drive to your preference, you will have a handy extra external unit for backing up to.

Keep tuned to the OWC Blog for updates…

Related Post: Diagnosing 2009 & 2010 iMac Fan Speed Issues After Upgrading The Main Hard Drive


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    1. Tdog says:

      So I just purchased a imac i5 2.66 ghz middle late 2009 model without a hd I Hope that I can fix it and make some cash. But in doing some research i am confused. Is it really as simple as stated in the third to last statement by Fred? Or is the best option still to short the temp sensor and run app? Or is there another option that is better? I don’t know what the original hdd was because I purchased it without a hdd. Was that a mistake?

    2. Lisa B says:

      I took my late 2009 imac in due to a smart error irreparable hard drive error when I tried to install mavericks. Since my 500 drive was almost full I decided to go,with a 1TB. well apparently they goofed, put a non compatible drive in and I had the fan thing going on, that is after they told me my optical drive was not working, which it was just days before I took it in, then to top it off the screen went black the next day. I feel like they did all this when working on it or by putting in the hard drive incorrectly, am I wrong for thinking this or could all this happen to 3.5 year old imac that has not seen much use since I got an ipad 2 years ago?

    3. Roer says:

      I’ve ordered an used iMac Late 2009 27 inch, 2.66 gHz i5 quad core. It has a replacement drive 250gb. I want to replace this with an hybrid drive, if possible. Since I don’t know the brand of the original drive, how do I figure out which manufacture (WD, ST, HT etc) to go with? ( I do have the serial number)

      Would it be correct to assume that whatever replacement drive (250gb) is on there is the same brand as the original (1TB) so long as the fan wasn’t going crazy? Stated another way, since a different brand would cause the fan to go crazy, any drive that doesn’t do this must be the original brand.

      If that is the case, my job will be a lot easier.

      Also, I plan to hire a pro to do the replacement. What’s a reasonable price for the labor part, if someone knows off the top of their head. (I’m in Jax, FL, if anyone is will to offer to do this.)

    4. justin says:

      i have a late 2009 27″ imac and my seagate HD crashed, too late for the apple replacement program. ive read many reviews of people buying internal seagate HDs that’ll crash within a few months. is there a way to change the thermal sensor in the imac to put in a WD HD?


      • Ben Morici says:

        We are sorry to hear your drive failed, it is never pleasant working with a failed drive. While we do not have a DIY Main hard drive replacement kit for the 2009 or 2010 iMac, like our 2011 kit, there are a few options. While it is understandable to be hesitant to get the same brand drive that has just failed, Seagate drives are very reliable and a brand we recommend.

        If you wish to pursue installing another brand HDD you can certainly do so, you will need to manage your computer’s fan speeds though. There are a few fan control programs available on the market such as SMCFanControl and HDDFanControl. However, OWC does not endorse using these programs for this purpose. The best solution is replacing your drive with an identical brand drive, and this is the solution we suggest.

    5. David says:

      I have a 27-inch, late 2009 iMac (3.06 GHz Core 2 Duo, 12 GB Memory). The drive is a a 1TB Sea Gate (ST31000528ASQ Media). Can I upgrade to the 2.0TB Desktop SSHD Solid State Hybrid Drive 3.5″ 6Gb/s 64MB Cache 7200RPM + Software Bundle?

      Also, I saw in a previous comment that you recommend professional installation. Does OWC have any affiliates/recommendations in NYC?

      • OWC Ben M says:

        All the testing we have done shows that if you replace the main drive with an identical brand drive it will work without issues. The installation is tough, so we do recommend a certified technician perform the installation.

    6. Yonatan says:


      i have 27″ late 2009 iMac and i’m planning to replace the hdd.
      i now have the 1tb wd disc, and i just bought the 2tb wd2002faex to replace.

      1. will it be compatible with my iMac model?
      2. do i have to jumper the 5 – 6 jumpers to lower it to 3gb/s or can i install it without jumpers?
      3. if i do use the 5 6 jumpers will it affect the termal plug?


    7. Pankaj Bhalerao says:


      I am from India, and I have a 27 Inch iMac (Mid-2010). The original 1TB hard drive (WD) of the mac is gone bust, and I need to replace the hard drive. The apple authorized service center here is charging exorbitant price for a replacement hard drive (Almost $340).

      Can I use any 1 TB WD Hard Drive as a replacement which is hardly costing around $100 or do I need to purchase only Apple Firmware loaded hard drive?

      And how should I proceed with installation of OS (I don’t have any DVD’s, etc)?

      Many many thanks in Advance.

    8. iWorld says:

      Hello, my iMac 21.5-inch, Mid 2010 have hard disk WDC WD5000AAKS-40V6A0 Media, My computer is heavily braked and I checked the disk with Techtool Pro 7 and it found more than 500 bad blocks , I want to replace it with a new one.
      Can I replace it with a newer model?
      If I replace , I will not have any problems with The fan speed of iMac ?

      • OWC Michael says:

        Yes, for the main hard drive bay, the “same for same” brand caveat still applies. As long as you stay with the same brand (even the newer models) you shouldn’t encounter any fan speed issues.

        • iWorld says:

          Yesterday i replaced my old HDD to new WD Black 1TB WD1002FAEX , but it’s without Apple’s firmware. After replacing Fans ran at full capacity and I’m using a HDD Fan Control :(

    9. 27 Inch Brick says:

      I have a late 2009 27″ iMac model 11,1. It has the 2.66ghz quad-core i5, Radeon HD 4850 and a 1tb drive. The hard drive ate it, abruptly, the other night, and running the disk diagnostics from the Os X install DVD confirms that the hard drive exhibits a mechanical failure.

      Without opening the case, is there any way of determining which brand drive I need to order? I’d like to get as little dust as possible in there, so I’d only like to open it up once for install.

      • OWC Eddie says:

        Use Disk Utility within your Mac OS X install disk to identify the type of drive you have. Within Disk Utility, in the left pane, highlight the disk drive in question . Once the drive is selected there is a section at the bottom of Disk Utility that says “Disk Description”. “Disk Description” will typically list the type of drive using either the company’s abbreviated form or by listing out the full manufacturer name.

        Examples of abbreviated names from hard drive manufacturers:
        Western Digital drives can be listed as: “WD” or “WDC” followed by the model series type
        Seagate drives are listed as: “ST” followed by model series type
        Hitachi drives can be listed as: “HT” followed by the model series type

    10. Robert says:

      I’m currently running a late-2009 27″ iMac i7 (iMac 11.1) with 16GB of RAM purchased from OWC. My iMac is also equipped with a OWC Data Doubler and Mercury Extreme Pro SSD (120GB) as a boot disk. This combination is blazing fast in comparison to the OEM 7200RPM hard drive. For those who haven’t done the “upgrade” to a OWC SSD I can confirm this: You are in for a treat; it’s a night-and-day difference.

      Now, the question is this: Will I see any benefit to going to an OWC Mercury Extreme Pro 6G compared to the OWC Mercury Extreme Pro that I bought two years ago? My understanding is that the SATA controller for the iMac 11.1 is only rated for 3Gb/S but I wanted to confirm with OWC techs before I make a decision.

      Please advise.


      A return customer

      • OWC Michael says:

        You are correct – the iMac11,1 has a SATA Revision 2.0 (3Gb/s) system bus, so installing a 6G SSD would still yield 3G speeds.

    11. Jonny says:

      Hello. I am new to this world of iMac customization, so please accept my apologies for any incorrect statements/stupid questions. I have a late-2009 iMac, 21.5″ screen, 3.06 GHz Core 2 Duo, 16GB RAM, 2TB Hitachi SATA drive.

      From what I have been reading it is possible to switch out the Superdrive and add another drive. I haven’t been able to find any instructions specific to my late-2009 21.5″ model, however. Does anyone have any leads/info that are specific to this model? Ultimately my questions are:
      1. If I CAN switch out the Superdrive for another internal drive, what kind of drive does it have to be? 2.5? 3.5? Does it have to be by a specific manufacturer? Any limitations in storage space? Etc.
      2. In addition, is it possible to switch out my current internal drive for an SSD drive so that the OS/apps load faster?

      Thanks ahead of time for any info/leads!

      • OWC Michael says:

        You certainly can swap out the optical drive for a 2.5″ hard drive or SSD with the OWC Data Doubler. We do highly suggest professional installation in the 2009 iMacs.
        As this article suggests, in order to swap out the main hard drive it needs to be replaced with the same brand hard drive. So in your case, you could upgrade that 2.0TB Hitachi Drive to a 3.0 or 4.0TB option for additional space, but a SSD in that bay is not an option without additional hacks or modifications. However, you can always install a SSD into the Data Doubler and set it as the boot drive in System Preferences.

    12. Audi says:

      Hi OWC Michael,

      Hi, i am wanting to replace my HD on my 27″ imac mid 2010, 3.2Ghz i3 model (the drive has failing SMART notice!!). Just before i order from you, can i please check if the following HD model will suit my imac? As in it will be compatible with the temperature measurement port etc.

      1.0TB Seagate Barracuda 7200.12 SATA 6Gb/s: 7200RPM, 64MB buffer with Perpendicular Drive Technology. Backwards compatible with SATA 3Gb/s and 1.5Gb/s. New with 2 year Seagate Factory Warranty. (ST1000DM003)

      I saw the recommendation from here: http://blog.macsales.com/2751-proprietary-cable-can-put-the-brakes-on-upgrading-late-09-imacs. Just wanna check if the recommendation’s still valid.

      Many thanks,

    13. Nate says:

      Do you have a tutorial video to replace the optical drive with an SSD drive for the late-2009 27″ iMac?


    14. Mark K says:

      I have a Western Digital Caviar Black 1.0TB SATA / 32Mb Cache HDD, Model No: WD101FALS-40U9B0 in my late 2009 27″iMac (10.1). I want to upgrade that to the new 4TB WED drive which you have http://eshop.macsales.com/item/Western%20Digital/WD4001FAEX/

      You do not have any installation videos for HDDs for the late 2009 27″iMac (10.1) despite the comment in the original post saying “As we were getting information together for the new iMac instructional videos, we came across …” See: http://eshop.macsales.com/installvideos/

      Can you please confirm that this WD 4TB drive will work with my late 2009 27″iMac (10.1) ie. 1. it will be compatible with the existing WD temperature controller cable 2. It doesn’t matter that the drives are now SATA-III (6.0Gb/s) and 3. that the Motherboard can support the higher capacity. I am running the latest operating system in Mac OSX but I mainly use Bootcamp Windows 7.

      • OWC Michael says:

        Yes, we have tested the WD4001FAEX drive in the 2009 iMac – it is indeed compatible with the existing WD controller cable and the drive being faster than the bus speed on the machine doesn’t cause any issues.

        • Jim Smith says:

          OWC Michael I just got off online chat with OWC and the rep said that due to the age of this article if I buy the Seagate HDD listed to replace my failed Seagate HDD and put it in my late 2009 EMC 2309 10,1 27″ IMAC that it won’t work with the temperature sensor. What is the final word since you are the main one following up on this article. My HDD dies a week after the free replacement program ends.

          • OWC Michael says:

            That’s actually not quite accurate and we’ll be reviewing this subject with our techs so there’s no confusion in the future.

            We are constantly testing and re-testing compatibility in our labs and the swapping of brand for brand in the 2009 iMacs is still viable – even with the very latest 4.0TB Seagate Desktop HDD ST4000DM000 Serial ATA 3.5″ 6Gb/s 64MB Cache Hard Drive.

            I actually revisited this subject in a post just this past February – the information hasn’t changed.

            If we find down the road that something does change, we’ll be sure to update our information. With the HDD manufacturers buying each other out, there’s likely to be some enhancements or changes in the future where specs for one brand may be applied to a subsidiary brand (or vice versa) – but as of yet, we haven’t found anything that invalidates the stance that you can replace the main bay HDD with another model from the same manufacturer.

            • Jim says:

              Thanks I just wanted to confirm with everyone after switching to the one terabyte Seagate hard drive offered on the website that it is 100% compatible with no issues with the fan in my 2009 iMac. There is too much misleading information in regards to people with 2010 2011 and 2012 imacs and confusing people with legitimate replacement options for late 2009 iMacs.

      • Yonatan says:

        Hey Mark,
        I’m going to do the same process and replace the 1tb wd drive to wd2002faex 2tb drive on my late 2009 uMac.
        just wanted to know if u did the process already and if u had success with it, just to make sure my board works fine with 6 gb/s drives….

        thanks in advance

    15. Mike Klausing says:

      I have Hitachi HDS722020ALA330 HD in my late 2009 27″iMac. I want to change out to the new 4TB drive. Can this be done using same brand?

    16. James says:

      I have a later 2009 iMac i7 2.8GHz that seems to be getting slower by the day, mainly due to HD access. After recently having put an OWC Electra SSD in my boss’s MacBook Pro and seeing the mind blowing speed increase, I’ve been growing more frustrated by the day with my spinning platter hard drive iMac at home. I really REALLY want to put an SSD inside it, but I would prefer NOT to replace my optical drive with one. I really want to just swap out my factory Western Digital 1TB hard drive with an OWC SSD. But my concerns are twofold:

      1) I’ve never removed the glass before. I understand it’s not hard and that OWC sells the suction cups required to do it painlessly. Even so, in a normal home environment (not a professional clean room), how is it possible to prevent dust from getting under the glass when you put the glass back on?

      2) The temperature sensor issue. The only interesting comment I’ve seen here is the fellow who reported success by adding a 470-ohm resistor “somewhere” on the hard drive cable. Is there really no one else who has tried that? What about you folks at OWC?

      I really, REALLY want an internal SSD in my 2009 iMac. Man do I want one. But again, I don’t want dust under the glass, and I want to make sure that normal, automatic fan control will be maintained, without having to rely on a less-than-reliable software hack.

      I look forward to your replies.

      Thank you.

      • OWC Michael says:

        1. A Microfiber Cleaning Cloth can clean dust form the monitor screen and the glass just before reassembly.
        2. We are proponents of the same-for-same (in regards to brand) HDD swaps in the 2009 iMac models and for replacing the optical drive with a Data Doubler in order to add an SSD to the system.

        • James says:

          Thank you for the advice about the microfiber cloth. I’m still a bit apprehensive about removing a huge pain of glass on my 27 inch iMac, but I will give your suggestion further thought.

          I can appreciate your DataDoubler solution for the sake of it being simpler than going about replacing the stock hard drive with an SSD. But the fact is that I use the internal optical drive of my iMac quite often. And although I am fully aware that OWC sells external optical drive solutions that exceed the specifications of the internal optical drive, it nevertheless is a fact that an external optical drive requires extra space on the desk, which in my case I really don’t have.

          For this very reason, I eagerly read through the comments in this thread to see if there could possibly be a rather straightforward and easy solution to swap out the stock hard drive with an OWC SSD. And out of all of the comments that I’ve seen here, the most promising one is from the fellow who says that he solved the problem with a 470 ohm resistor. For me, soldering in a resistor and putting some heat shrink tubing over it is a very easy solution. I also consider it a far more reliable solution that a software hack that may not work reliably in the long term to keep fan speed under control. The main reason I commented here is because there’s only one person who reported that a 470 ohm resistor would work. I would think that if such was true, I would see other people reporting the same success, either here or in other forums around the web. And that’s why I’m curious if OWC has experimented with the resistor trick, especially since so many iMacs come through your hands and you’ve had a chance to do experiments on them.

          If you have any further thoughts to share, I would certainly appreciate hearing them.

          • gmmd says:

            Same boat as u James. I have a Hitachi 1TB in my late ’09 iMac. Thinking of trying what ‘revat’ said in post from July 9, 2012.

            If u try that, be sure to post up here if it works. I’ll do the same when/if I get around to upgrading to an SSD.

            • gmmd says:

              another possible hack is to use the optical drive cable/sensor as stated here (assuming the pins are the same configuration) link comments seem to indicate a possible change and/or multiple connector possibilities. http://www.digitalintrovert.com/2011/09/03/how-to-upgrade-hard-drive-late-2009-27-imac/

              • OWC Michael says:

                Actually, each hard drive manufacturer has a different pin configuration – see my comment from March 2010.

            • James says:

              I’m not going to try anything yet because I live in Japan and international shipping is too expensive to just return the drive if my test don’t work out. That’s why I really need to know what’s going to work how to implement BEFORE I buy.

              So for now I’m simply waiting for a reply from the fellow who reported that a resistor would resolve the fans spending problem. Either his report was bogus, or he’s fallen off the face of the earth. And since no one from OWC has commented on that specific point either. It’s clear that they don’t know, nor have they experimented with resistors, nor do they seem interested in trying.

              All said, I still want internal SSD inside my October 2009 iMac very badly, but I don’t want to remove my internal optical drive to accomplish that, and I don’t want a solution that will not reliably keep the fan speed in check.

              So I wait, and I watch this dialogue continue…

    17. Doug says:

      Re: Imac 27 I7 late 2009

      Will the newer 4TB WD drives work as a replacement if I already have the wd 1TB drive?

      Also are there any issues on replacing the optical drive with a SSD ?

      • OWC Michael says:

        In the 2009 iMac models, as long as you’re replacing the original drive with the same brand drive (as you are, WD for WD) then you should be ok.

        Replacing the optical drive with an SSD in that model does require use of our OWC Data Doubler Optical Bay Hard Drive/SSD Mounting Solution.

      • Zachariah says:

        Not sure about the Hitachi drive but I have replaced my optical drive with an SSD and encountered absolutely zero issues. Worked beautifully. I used the DataDoubler to hold the drive and just plugged in the cable. It has made a tremendous difference in the speed of the computer.

    18. freediverx says:

      I need to replace the failed Seagate HD on my late 2009 27″ iMac. After encountering endless threads on the hard drive compatibility issue I wound up here. Unfortunately, this article hasn’t been updated since it was posted in Nov 2009, and 2 of the 3 suggested replacement drives are listed as “Sold Out.”

      What are my choices if I want a 1.5TB or 2TB replacements drive?

    19. Zachariah says:

      In my late 2009 21.5″ iMac I replaced the optical drive with an SSD, leaving the stock 2Tb Hitachi drive. I’ve begun to enjoy the complete silence when the hdd spins down and I can just work off the SSD. Anyone have any luck with replacing the 3.5″ drive with a 2.5″ drive? Just wondering about cable adapters, temperature sensors, drive caddy, etc. to pull this off.

      I only have 200Gb on the 2Tb drive so even if I popped in a 500Gb or 1Tb 2.5″ drive I would have plenty of space for my needs.


      • Jonny says:

        I have the same system and am looking to do something similar. I’m guessing you have the Core 2 Duo as well? When you replaced the Superdrive with an SSD drive, were you able to make the SSD drive your main boot drive? Thanks!

        • Zachariah says:

          Yes that is correct. When you start up your mac you can select which drive is your start up drive. It was well worth the trouble. I use the the 2Tb HDD for archiving, backing up the SSD, my music, etc. to keep only important things on the SSD like my OS, programs, work files, etc.

          You can also turn the SSD and HDD into a hybrid drive. There are instructions on the internet for doing that. That way you can have a very large, fast drive. I chose not to go that route because the HDD is the original that came with the computer and if it should go, it takes the data on the SSD with it.

    20. Lou A says:

      In the above article it states:

      “To determine what brand hard drive your iMac has, go to About This Mac, click on Serial-ATA, and then look for the drive model installed at the factory.”

      My IMac has completely crashed therefore i can not access the About This Mac feature. Is there anyway other way of determining what brand hard drive my IMac is using??


    21. Pete says:

      How about for iMac 2011. Model A1311.
      Is there a cable for the hdd fans control.

      i haved change my hdd with the same brand (WD). Just with some better spec. Higher GB for more space.
      I found one with S.M.A.R.T and the fans went not so crazy like to take-off iMac. Only small noise from the fans.
      When i tried AHT. The iMac failed and sayed it cut not control the fans.
      So it is very close to sole my problem.

      So is there cable or a SW issue or wrong select hdd.

      • Franky says:

        Hey all guy, I solved the fan problem, try “SSDFanControl 2.1″, it is free and work very well. Good luck guy. ;)

    22. revat says:

      Just to let everyone know, my 1TB seagate died. I replaced it with a SSD. I unscrewed the circuit board from the dead drive and plugged the thermal sensor back into it. With the smaller size of the SSD there is plenty of space to just leave the old drives circuit board in the imac. Works great, no fan issues at all.

      • Macha camacho says:

        Yes mine to 18 mo.old more options with mid ten 27″ maybe gods will,si?ssd:)

      • chuck says:

        revat: so your SATA cable is now connected to the SSD and the thermal cable is still on the dead 1TB drive u left in there?? what SSD u got in there? 3Gb or 6Gb? please confirm, thx!

    23. jesush20 says:

      - iMac 27″ late 2009.
      - Segate 1Tb HD dies, ST31000528ASQ.
      - Changed by a Western Digital 2 Tb, 64 Mb cache, Green Caviar.
      - The annoying fan issue.

      I just install smsFanControl and It did not response to the terminal command, so the fan went crazy still. To solve this I reset PRAM, and now it obeys to the terminal command: /Applications/smcFanControl.app/Contents/Resources/smc -k F1Mx -w 12c0

      This make the fan 1220 rpm and the HD temp is 47º C right now.

      • jesush20 says:

        Finally, I insert a a 470 Ohm resistance 0.5 Wat in the sensor connectors and everything works fine, even passes the Apple Hardware Test.

        Now there is no problem when the iMac go to sleep and losses the information to keep the fans working at 1000 rpm.

        • James says:

          I’m curious about how exactly you connected that 470-ohm 1/2W resistor to calm the fans. Did you use a single resistor? If so, on what pin? Do you have a photo or schematic?

          Also, does that resistor keep the fans running at a fixed speed all the time, or does it simply prevent the fans from spinning too fast? (In other words, does that resistor allow normal, automatic fan speed control so the fans spin slow when the computer is cool and then ramp up when the computer gets hot?)

          I look forward to your reply.


      • jesush2o says:

        Today I’ve received a mail from Apple.
        They say that some iMacs sold from October 2009 and July 2011 are having problems with the hard disk, so, they are going to replace my hd.
        A bit late.

    24. Joe says:

      Has anyone tried flashing a like model drive with http://support.apple.com/kb/DL1378?

      I believe that is a drive firmware update, not an efi firmware update.

    25. Gabriel says:

      Hi. I found the component behind the HDD thermal sensor. The component is MPS3904 transistor, or 2n3904. I’ll try mount one cable. If works, I will post the results and tests!

      • Chal says:

        YEPPP!!! I replace the hdd side connector on sensor cable tó a 2n3904 transistor, and evrything is fine!! :)
        My 2009 late iMac passes the Apple Hardware Test (AHT), and the HDD fan is silent (1000-1100 RPM).

        • Chal says:

          IMPORTANT: Wire trick (swap the black and the gray cable), and plug in to the replaced (retail) HDD is NOT SOLVE THE PROBLEM!

          This action results a short circuit, and infomrs the SMC that is the HDD bay is off. This is a very good solution for the SSDs, but not for the HDDs, because the cooling system is not raise the HDD fan’s RPM when necessary (if the hdd is warmed up).

        • Johan says:


          Would you care to explain exactly how you did. And if this fix is working for WD or Seagate drives (or both)?


      • psyxoo says:

        any news ?

      • JEH says:

        Could you please explain how the leads on the transistor go to the sensor plug?

    26. Katra says:

      Loud Fan Problem – SOLVED – COMFIRMED..!!!!!!!

      Hello guy’s .. i just upgraded my hard drive on my 27″ iMac from a 1TB to a 2TB..( Seagate )… and as you would expect.. i ran into the the loud fan issue where it starts slow and then goes full blast and stays that way. Well as “Diesel87″ posted in this page..he performed a wire trick where he swaps the grey wire to the black wire and vise versa. This absolutely worked !!!!!!! I no longer have a loud fan anymore and everything is back to normal..!! I check it with the iStat application for mac and it gets the correct thermal temperture and fan speed for the hard drive. Im so glad i stumbled into this page cause it truely fixed my loud fan issue!! if you have this problem do the wire trick..though you might need some small pliers and patience..but it pays off..!

      Thanks and i hope this helps..!!

      - Katra

      • Seitzberg says:

        Do anyone know if the cabletrick is usefull in a late 2009 imac 21,5 ???
        Or have anyone testet the cable in the 21,5 model…?

      • jpn says:

        I’m considering to upgrade my iMac Late 2009 21.5″ HD to Barracuda XT 2TB ST32000641AS.
        Did you use the same Barracuda XT model for your 27″ ?
        There are four pins on the connector, but did you only use the two original pin locations, and just swapped the grey with black?

    27. Trevor says:

      Can someone please confirm for me this? If my Late2009 27 inch Seagate died, repalcing it with a WD Green HD will require a new cable. I found this cable: https://www.usedmac.com/products/922-9225-imac-27-western-digital-hard-drive-temp-sensor-cable

      Issue that I can see is buying this cable doesn’t mean it will work right either. Sorry to sound lame but I’m getting confused messages. Do I need the cable AND software fix or will just the cable make my “Seagate” iMac work with a WD Green drive?

    28. TakeABiteOutofApples says:

      I replaced my late 2009 imac with another seagate HD (not a model listed). but i can verify that replacing the with the same model doesnt necessarily mean that the sensor is still going to work..going to try the 922-9229 Optical Temp Sensor Cable route…

      btw if you want to go the software route…. HDD control fan did work instantly…

      • thomas says:

        @Takeabiteofapples Same here I have 10.1 late 2009 27′ and bought what OWC stated as correct one but temp sensor does not seem to work properly. Did you already try the temp sensor cable? IMHO that is the best solution rather then software one.

    29. Andrew D says:

      I have a late 09 imac. Want to replace the current seagate drive in it with a seagate 3tb drive ST33000651AS. Will this work? Please let me know.

    30. Chicco says:

      I’ve got a problem with my 1TB HD ST31000528ASQ in my 27″ iMac (late 2009).

      Is it correct that when i buy a 1TB HD from Seagate –> ST31000528AS AND the 922-9229 Optical Temp Sensor Cable that i won’t have any problems with my fan?
      I mean, when i buy the Optical Temp Sensor Cable do i also need the Apple customer firmware?
      I asked a Apple store over here and the OEM HD would cost me 286,90 Euro OMG !!

    31. Chris says:

      This is so confusing – I read somewhere else that as long as you buy the correct model ST31000528AS (as this post suggests) it has the correct firmware (AP24) – but others are suggesting it doesn’t? Or are we just talking about people who are switching brands?

      If I order the replacement ST31000528AS – will it work without hacking the temperature sensor. So a like for like replacement.

      As an aside If you send it to an authorised repairer, what do they do – order the Apple branded drives from Apple? How much more do they cost!?

    32. bmc5311 says:

      If you buy the replacement drive from OWC you will need to buy HDD Fan Control to correct the runaway fan issue.

      It works.

      And the way I look at it, $70 for the drive from OWC and $30 for the software, you’re still way ahead of the game.
      The Apple Store will replace the hard drive for $200-$300 ( no apple care – and they wouldn’t give me an exact quote), the one local Apple Authorized Service place (Mac Specialists, Virginia Beach) wanted $500 to do it.

      Seems like a rip-off to me, Apple should either make the firmware available or not use it.

      • DaveC says:

        Was your replacement a WD or Seagate.
        It’s supposed to be plug & play if you make the exact replacement/size upgrade listed in the article.

    33. Michael says:

      Here is the solution:

      Apple installs custom firmware on their hard drives. So even if you order one of the temperature sensors mentioned above, your fans are still going to be running at full blast. (And if you take your iMac to an Apple Authorized Service Provider, it will fail all of their testing)

      You can install an optical drive temperature sensor cable from previous generation iMacs. This attaches to the hard drive like older iMacs did (to the top with a piece of tape basically). Now your iMac will be able to correctly read the temperature of the hard drive, causing the fans to run normally. And, when running Apple Service Diagnostics and the Apple Service Toolkit at an AASP, it will pass all the testing.

      The part you need to order is: 922-9229 Cable, Temp Sensor, Optical. Its cheap.

      I have used this cable on an iMac (21.5-inch, Mid 2010) and it works great. Though, I haven’t tried it yet on other models yet, it should work just the same.

      Good luck!

    34. Diesel87 says:

      Hey Guys,

      I´ve got THE solution for replacing the standard HDD with an WesternDigital Drive.
      First you need the named WD-adapter(Part No. 593-1062). The trick is: You have to put the adapter invert onto the Jumper-Interface so the grey cable is connected to Jumper-Pin4 and the black cable to Jumper-Pin3.
      When you´ve got an iMac with an WD drive the adapter is connected grey on Pin3 and black on Pin4. Thats all.

      The lenght does´nt matter. Only the right direction ist important. I´ve done an mistake when I ordered the adapter, so I got an adapter for the 21″ iMac. But it works also…

      So good luck with replacing your HDDs with WD drives.
      After all I can only advise you to use WD drives. At my work I had in two years about 7 failed HDDs – All of them where Seagates… So decide the maufacturer your own. In my oppinion WD is the better choice…

      Have a nice day

    35. Michael says:

      Here is the solution:

      Apple installs customer firmware on their hard drives. So even if you order one of the temperature sensors mentioned above, your fans are still going to be running at full blast. (And if you take your iMac to an Apple Authorized Service Provider, it will fail all of their testing)

      You can install an optical drive temperature sensor cable from previous generation iMacs. This attaches to the hard drive like older iMacs did (to the top with a piece of tape basically). Now your iMac will be able to correctly read the temperature of the hard drive, causing the fans to run normally. And, when running Apple Service Diagnostics and the Apple Service Toolkit at an AASP, it will pass all the testing.

      The part you need to order is: 922-9229 Cable, Temp Sensor, Optical. Its cheap.

      I have used this cable on an iMac (21.5-inch, Mid 2010) and it works great. Though, I haven’t tried it yet on other models yet, it should work just the same.

      Good luck!

    36. Reino Karvinen says:

      I have 27″ 2.66MHz i5 iMac with the HDD fan operating at 4200RPM. I have upgraded to a 2TB Seagate Barracuda XT drive (Seagate 1TB was originally installed). I notice that since the last SMC firmware update my HDD fan has been blasting away, also the battery status being reported for the wireless mouse and keyboard in control panels is inaccurate. It is reporting 100% for the mouse when the actual is 56% (reported by iStat Pro) I am using rechargeable batteries and I know they never report 100% even when fully charged. And the keyboard status also is incorrect.
      I am quickly coming to the conclusion there is a SMC firmware issue affecting various 27″ iMac’s.

    37. Tintin says:

      svenc: thanks for sharing, your swap wire trick worked for my 27″ iMac too. I swapped the failing stock Seagate 1T for a new Seagate 2T. Even though the heat senor plug is identical the fan keep blasting at 5000rpm and iStat Pro returned “–” for the HDD temperature.
      I swapped the two wires of the plug (see svenc’s post above) with the help or a paperclip, and it now worked. Fan spinning at 1133rpm and I get normal reading from iStat on the HDD.

      • Pete says:

        I have a mid 2010 27″ iMAC 11.1 with 1TB Seagate HDD. Received email from APPLE on 25October2012 to say these drives are failing and will be replaced free of charge by APPLE. Only problem is my nearest APPLE service centre is 250km away and APPLE refuse to send me the HDD itself so I can do the swop myself. It was cheaper to buy a new HDD locally and swop it out than drive 500k m and spend a day away from home. I tried the 2TB Seagate Barracuda XT, model ST32000641AS – 9GV168-301 with firmware CC13 but the fans went ballistic. I removed the XT and replaced it with a 2TB ST2000DM001-9YN164 that I had flashed to firmware CC4H on a windows XP machine before I placed it into the iMAC. HDD fan is running normally and quiet. Shows up in iSTAT as 1238 rpm at 50 C while I am doing a CCC clone onto the new drive. I also ran the Seatools Dos bootable CD on a windows machine and did all the Seatools Tests on the new drive and it checked out OK. I did NOT have to swop the grey and black leads as some posts above mention. Just plugged everything in the way they were on the old 1TB Seagate and everything works.

        • JEH says:

          The free and simple solution is to use SSD Fan Control from http://exirion.net/ssdfanctrl/
          I used this little app on a 21.5″ iMac that had a replacement HDD and it works really well. HDDFanControl pricing is stupid, it costs more than Mountain Lion! Try SSD FanControl and send a couple of euros to the developer, surely he deserves it.

        • JEH says:

          I would be concerned that the CC4H firmware is part of the problem with these drives and that you have just turned a good new HDD into another bad one?
          But I would love to know how you managed to transfer the firmware, if you’d care to share?

          • Pete says:

            Hi JEH, I did not “transfer” the firmware from the old 1TB drive to the new 2TB. I just flashed the new CC4H firmware for the 2TB HDD that I downloaded from Seagate website. I did that by making the Dos bootable CD (also downloaded from Seagate) and by plugging the new 2TB drive into a Windows PC with an Intel mobo (old P4 machine). Then booting of the DOS CD , I was able to flash the new 2TB drive. I did not use any proprietary APPLE firmware for the flash – just that standard firmware from Seagate. The 2TB seems to be running well but it is a little warmer (48 – 52C) than the old 1TB drive. There are no issues with the fan speeds though. The HDD fan is quiet and running at 1500rpm via SMC fancontrol. Ramping up the rpm’s to 2000 does nothing to cool the drive down. It stays around 50C. Does that answer your question?jawsdrie@yahoo.com

    38. FrankyChing says:

      Hi Scott, could you please share some photo? I have one 2.5 inch HDD, it also come from my MacBook. I want to do same.

    39. Scott says:

      JuNK @ post #107, you are a genius. I bought a new 1.5 TB WD Green to replace the thunk thunk thunk of the 1 TB Seagate that came with my Mid 2010 quad core iMac. Sure enough, different connector for the thermal. Thank God I read through far enough to see your post…I grabbed an older 160 GB 2.5 inch Seagate that came with a MacBook, slapped that on top of my new drive courtesy of some cushiony double-sided tape, and plugged the thermal cable into the old Seagate. Everything fit perfectly, no problems, and the new drive works with NO FAN ISSUE WHATSOEVER. In fact, the fans spin up normally when they need to (I am using SuperDuper to copy the old drive to the new…heavy work) and have only gotten to 1400 before spinning back down normally.

      Thanks again for your find. You are my hero.

    40. Ryan says:

      I’m a bit late in the game but our offices just received five 2009 model 27 iMacs. I’m planning to purchase a few OWC Mercury SSD to replace the hard disk. May I ask how difficult is the switch? Or probably it would be more advisable to simply keep the 1 tb drive and buy the iMac data doubler and replace the ODD?

    41. FrankyChing says:

      Hi Tintin, I don’t know about seagate, because my 1TB HDD is using WD. It only 2 pins.

    42. Tintin says:

      Thanks everyone for their inputs. I’ve recently changed my Seagate 1T with a Seagate 1.5T. The 4pin sensor socket fits the original cable but probably due to the firmware the logic board is not picking up the signal. The HD fan blasts at 4500 rpm.

      I’ve tried the commandline code with smcFancControl app and it works like magic, though it was said that you have to run everyone after your mac sleeps.

      Franky, can you share how to DIY the 2n3904 temp sensor? I heard it’s shorting the Base and Collector – but then connect which end to which pin (seagate connector is 4 pin)?

    43. FrankyChing says:

      Tom Yanckowitch, could you please share your’s ?

    44. Alan says:

      @ Tom

      Please share the command line code – I have a 2TB WD with HDD fans at their max (mid 2010 27″ i7)

    45. tom Yanckowitch says:

      Torstein you have really done your homework. Thanks for this input. So now I know that because I managed to spin down HD vent to 1100 rpm I can be still safe from any overheating.

      Yes I said it!! I found fix and made my crazy fan go down! I used smcFanControll app and a comand line in Terminal.

      It works as magic! I am happy there was no need for some service guy poking around my mac!

    46. Torstein says:

      I think it’s safe to short the temperature connector, even for regular hard drives (non SSD). Because it takes real abuse to make the hard drive fan speed increase. In practice, hard drive fan speeds over 1100 rpm isn’t necessary.

      I’ve reached this conclusion after extensive testing of a 27″ Core i7 late 2009 iMac, and a 21″ Core i3 mid 2010 iMac. With a stock (Apple branded) 1 tb Seagate Barracuda 7200.12 drive inside both computers, and the machines under heavy, continous load for several hours, the CPU fan went faster but the hard drive fan was just hovering around 1100 all the time. Like it would have done, had I shortened the temp wire. I used TemperatureMonitor to watch the temperatures, and SMCFanControl to watch the fan speeds.

      What I did was this: I duplicated lots of files, making the hard drive work intensely for hours, and at the same time repeatedly converted a HD movie (from iso file) to .mp4 with Handbrake, totally maxing out all the CPU cores. The temperature of the hard drive was 49 degrees celsius at the most for the 27 inch and 53 degrees for the 21 inch. Room temperature was normal, 23-24 degrees celsius.

      To see if maybe the CPU fan was cooling also the hard drive, I eventually ended the Handbrake conversion process, just keeping the file duplication going, and the CPU fan spun down to normal speed, but the hard drive fan did not spin up. I waited an hour to see if it changed speed, but nothing happened.

      To find out what would happen in a really hot environment I placed the 27″ iMac on the radiator in my living room to see if the warmer conditions there had an impact. I took the temperature right outside the middle of the screen, and it was 37 degrees celsius. I did the same test as described above, and the CPU fan went higher this time (almost 3000 rpm) but the hard drive fan was again just hovering around 1100 rpm. Temperature on the hard drive reached 55 degrees.

      However, on the next day, after the iMac had sat on top of the radiator the entire night, I tried again, and this time the temperature reached 58 degrees, which triggered the hard drive fan. The fan went from 1100 rpm to 1300 rpm. I couldn’t get the temperature higher than that, even after several hours, and when I ended the Handbrake conversion, the hard drive fan went back to 1100 rpm, with the file duplication still going strong.

      I bought the Hitachi Deskstar 7K3000 3tb disk and installed it in the 27″ iMac, then tried the test again (on the floor, not on the radiator). This disk is both warmer and noisier than the stock Seagate Barracuda 7200.12. It reached a max temperature of 63 degrees, and the seek noise was more obvious (but it’s still pretty quiet behind the iMac’s screen).

      My conclusion is that for light and moderate use of your iMac, you can safely buy and install any hard drive. Short the temp wire, you’re not gonna need it. For really heavy use it’s safest to go with disks that is not hotter than the stock Seagate Barracuda 7200.12. At the temperature this disk generates, and below, the fan never spins up anyway. But if you want a hotter disk, you can argue that even if you shorten the disk’s life a bit when you constantly run it hot, the speed you gain make this tradeoff rational. You can always use an external Time Machine backup disk, then you’re safe, no matter what.

    47. tom Yanckowitch says:

      Yesterday 14 feb.2011 i got delivered brand new 27″ Imac 2010 i5. Afeter 10 min. into using it I noticed fans and air stream from the back that was unusual for idle iMac.

      I came across tis site and read Petes post that describes my problem too! Once booted the fan will begin running at ~ 2500 RPM. It will continue to increase in speed until it reached very near max speed….. not quiet.

      Running hardware diagnostics generates error 4SNS/1/40000000:TH00-9.000

      Serial ATA check informed me that I have !!!SAMSUNG!!!! HD !! and that is in original factory sealed and delivered mac!

      What can I do about this? I cant stand the fans!!!!
      I got faulty iMac on arrival. Apple said they would service it but I am not excited on a machine that needs service upon its first boot up!!!

    48. mpa says:

      27″ Imac 2010 i7, anyone used the Seagate Hdd 2Tb 64mb cache ST32000641AS 7200rpm. for upgrade?
      Any problems with fan speed?
      Original HDD is 1tb seagate ST31000528ASQ
      What about the 2tb firmware? Any problems with fan speed on new drive?
      Tha sensor cable connector is the same, but don’t know about firmware.

    49. Torstein says:

      Found this on the Apple discussion board. It basically confirms that Apple has a special firmware on Seagate drives. It is not 100% sure that this firmware make standard drives unusable (because of the fan problem) but it seems like it:

      “I bought HDD ST31000528AS for my iMac, but without correct Firmware AP24, it is not work correct in my iMac. Please give me a link for ISO disc with firmware AP24.

      My HDD is working, but without AP24 firmware iMac can not get correct thermo data from jumper connection. That is why fans going to fly away…


      Got reply from Seagate. About Apple’s HDD and firmware AP24.

      Thank you for contacting Seagate in writing.
      The firmware is only available from Apple. It is specific firmware they have made available for the drives to work with their system. You will need to contact Apple about this problem.”


    50. Fred says:

      According to a post on today’s Macintouch Apple forum, all you need is the correct temp sensor cable, which can easily be ordered on the Net.

      *** quote
      Flat-panel iMacs used to have a temperature sensor attached to the hard drive. Without this sensor attached the fans will run full as they have no way of knowing whether they actually need to be cooling or not, and therefore err on the side of safety. Newer hard drives have the temperature sensor built in to the hard drives themselves. Each manufacturer is free to use any pin configuration they choose. If you change the brand of hard disk you simply need to order the correct temperature sensor cable for the new drive. If you use a manufacturer that Apple doesn’t use then you need to wire the cable yourself.

      Apple use the following 3 brands:
      Hitachi (hard drive sensor cable Apple part number 922-9223)
      Seagate (hard drive sensor cable Apple part number 922-9224
      Western Digital (hard drive sensor cable Apple part number 922-9225)

      AppleComponents.com has the Hitachi cable for US$19.

      Is the true fix as simple as this? No proprietary firmware involved or sensor machinations involved?

      • tampaappleman says:

        Hi Fred,

        I read your post about the Hitachi sensor cable and used it in my iMac with a 3TB Hitachi drive. It will NOT fix the problem with hard spinning fans. When the imac is cold the fans start spinning at 2500 rpm gradually increasing to 5500. HD temp is only 43 C. Please send me a link to the original Apple post. There is got to be a fix.


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