After replacing the hard drive in my 2009 iMac 27", I noticed that the hard drive fan spins at maximum speed since the sensor cable is not plugged in. (The new SSD drive doesn't support it)

To solve this issue, I installed a software called "Macs Fan Control" that can read out the temperature from the SMART status of the drive and control the fan speed itself.

This was a near-perfect solution until I upgrade my system to macOS Sierra. Now both "Macs Fan Control" and also "smcFanControl" can't control the fans anymore and the latter reports that I am running it on an unsupported system.

Now my question is, can I somehow control the fan speed manually using Terminal etc. or do I have to "trick" the sensor hardware-wise?

  • SpeedFan. or SMC fan control
    – OzzieSpin
    Oct 20, 2016 at 9:40

4 Answers 4


I am a firm believer in avoiding software "hacks" to fix hardware issues. To fix this problem, you need the sensor. Unfortunately, as you have found out, your SSD doesn't support this connection.

However, OWC makes an digital inline temperature sensor. Basically, it goes between the SATA power cable and the SATA power connector of your HDD/SSD. The temp sensor goes on your drive.

The best part about this is that it's a "once-and-done" solution meaning future OS upgrades won't be susceptible to software incompatibility problems like you are experiencing now.

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C|Net did an article on this exact problem and a review of this solution.

  • That's quite a nifty solution which I haven't heard of before. But I am not sure if it is worth investing in a 6 year old Mac..
    – comfreak
    Oct 20, 2016 at 9:44
  • 1
    I bought this for 50 bucks, being quite skeptical, but it actually works. My 27'' iMac is like new!
    – john
    Feb 8, 2017 at 11:57

Try SSD Fan Control and you might need an SMC reset.

It works just like Macs Fan Control but it supports Sierra. I have this installed on my Late 2009 iMac with a Samsung SSD and it works.

Hope it works!

  • You might want to explain how this product will help.
    – Allan
    Mar 1, 2017 at 13:16
  • works just like "Macs Fan Control" but suports Sierra, i have it installed on my imac late 2009 and a samsung ssd. works for me:) sorry for the short answer my english is soso :)
    – Chris
    Mar 1, 2017 at 15:58
  • For future reference, you need to add the details to the answer directly - I edited your answer as an example. It's also good if you review How to Write a Good Answer
    – Allan
    Mar 1, 2017 at 16:14

The internal thermal sensor of the (former) HDD can be replaced by a discrete thermal sensor which is to be fastened on your new drive (by adhesive tape or so). You can use an optical disc drive thermal sensor cable for that, it has the same sensor. The Apple part number is 593-0493, it should be available below 10€ (or 10 US$).

Because the sensor is just a standard transistor called 2N3904 you could even solder that cable yourself. Typically the former internal sensor connection cable consists of a gray and a black wire. The gray wire goes to both the base and collector terminals of the transistor and the black wire goes to the emitter terminal. Please be sure to insulate those connections properly and fix the transistor to the new „drive“.


You need to short the sensor plug cables. This is how people normally do it. Just pull the plug off the end and then strip the wires, twist them together, and use electrical tape or similar to protect them from the rest of the computer.

  • 1
    oh my god.... you just leave. the sensor's cables are most likely an i2C or similar serial interface, if you short those together, you'll get one unhappy iMac. I can't believe you even considered commenting such a thing but I’m an electrical engineer so perhaps the danger here isn’t obvious to all.
    – OzzieSpin
    Oct 20, 2016 at 9:42
  • 1
    Obviously you don't know much about this area. Take a look at forums.macrumors.com/threads/…. Oct 20, 2016 at 21:16
  • 1
    And "sensor wires" yeah that sounds like a serial or other data interface... what are these wires responsible for? Seeing as you know so very much
    – OzzieSpin
    Oct 21, 2016 at 5:54
  • 3
    Man, talk about luck. Shorting two wires that bypasses (most likely) a circuit that varies the voltage going back to the SMC and tricks it into thinking "all's well" and to spin down the fans. Just because the SSD doesn't generate the heat a HDD does doesn't mean they can't overheat. I wonder what gizmo Apple put in their computers to prevent devices from overheating by spinning up the fans...oh wait...a temp. sensor. You should pay attention to @OzzieSpin as the people on the site you referenced are the ones who don't know much about this area. The sensor is there for a reason.
    – Allan
    Oct 21, 2016 at 11:08
  • 3
    The OP fitted an SSD which runs massively cooler than a rotational disk, and this sensor is there to control cooling for the hard disk. The sensor is no longer required. Perhaps I should put that in bold and italics because you like that: The sensor is no longer required. Oct 26, 2016 at 7:43

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