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Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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Faulty CPU/ODD sensors or fans after Dual Drive Kit Upgrade


I performed the Dual Hard Drive Kit upgrade as suggested in the guide at Installing iMac Intel 27" EMC 2429 Dual Drive Kit (HDD or SSD)

I followed the steps precisely during the whole process.

After the second drive (SSD) was installed, I booted up the iMac and heard loud fan noise after a few seconds. Both CPU and ODD fans are running at full speed.

I have tried resetting SMC/PRAM, but to no avail. I reassembled the logic board twice, with and without the Dual Drive Kit upgrade. It still didn't fix the problem.

So, I believe something somewhere has gone wrong and I need to identify the problem and fix it.

I have also noticed that it is not just the fans that are loud, my game which I play every day at 30fps, is crawling at 6-7fps after the upgrade (still utilizing the HDD though, not the SSD).

Running the Apple Hardware Test revealed failure with TA0P code, which indicates Ambient Temperature sensor/connector failure according to some google search results.

Moreover, Temperature Gauge Pro app reports the following:

ODD 3729 RPM

HDD 1097 RPM

CPU 3917 RPM

Fan Diagnostics: These fans appear to be not working properly : ODD

Sensor Diagnostics: These sensors appear to be not working properly : CPU

Some further Googling has revealed that this person had a similar problem and flipping the LCD Thermal Sensor Cable fixed it for him: http://forums.macrumors.com/showpost.php...

However, I'm not sure which of the cables mentioned in the iFixit guide are the LCD Thermal Sensor Cable, for me to give it a go (I doubt any of the cables can be flipped on this model though).

Any help would be appreciated.


  • After installing 2nd drive (SSD) on 2011 27'' iMac,
  • CPU and ODD fans are running at full speed, HDD fan at normal.
  • Degraded gaming performance at 6-7fps.
  • Failure in Apple Hardware Test with code TA0p.
  • Something somewhere went wrong in assembling/disassembling (perhaps).


Update (02/25/2014)

I removed the LCD panel from the iMac and booted it with external Cinema Display. The fans are still loud. So I doubt that the problem is with LCD sensor. Maybe I should pay attention to the Ambient Sensor/connector, since the AHT failure also reported a fault with that.

Ответ на этот вопрос У меня та же проблема

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Hi, I have the same issue with ODD and CPU fans in my imac 27 mid 2011,

Do you find any solution so far? Thanks


10/17/15 See my answer below


Did you ever resolve this Gurpartap? I'm experiencing the same issue after adding an SSD to my mid-2011 27" iMac (although I also replaced the main HDD with a new HDD at the same time).

I've taken the SSD out and put the original HDD back in, and still get the TA0P failure in Apple Hardware Test.


@itspaulkelly Haven't found any solution yet. Tried Apple service centers, was advised that I replace the whole logic board. Meanwhile, "Macs Fan Control" app is keeping it quiet. It's the only app that has been able to control the fans in my case.


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I had this issue recently and after analyzing the schematics for the iMac 2011, I found that two tiny inductors (ferrite beads) in the ambient temperature sensors' path have been knocked off somehow and that caused the ambient temperature sensor not to work and in turn the system sped the fans up and slowed the cpu down. This issue has nothing to do with the hard drive it just happens to many people while they're disassembling the machine, the two inductors are right near the ambient temperature sensor connector (L5500 & L5501) and I guess can be knocked off easily. It can be fixed with some soldering skills and there's no need to remove the logic board for the repair. I don't think there is a need to replace the parts they're just there to reduce some radio frequency. If you do want to replace them they're both a 220 ohm ferrite bead SMT size 0402 (1005 metric).

After my discovery I found some guys on a repair website mentioning a few times that they've dealt with this issue on the iMac 2011.

That fix that was mentioned about the LCD temp sensor being inserted incorrectly was only for the iMac 2010 based on what I found in the schematic for that machine.

This is a picture of my repair, I just added two traces of solder to replace the missing ferrite beads.

Block Image

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Good Catch!

I tend not liking bridging across pads as there was a reason the component was put in to start with. Chokes are often used to control noise (EMI & crosstalk). I would recommend you try to find replacements as you never know!


Great discovery!! Suddently there is hope for my Mac again.. :) did soldering fix your problem? Can you see the temp value now? And are your fans and CPU performance acting normal now?


All the temperature sensors on the iMac connect directly to a temperature sensor management chip which is an EMC1428-7. The schematics for that chip don't mention the need for those inductors for it to operate correctly therefore I figured that Apple just placed them there for extra caution and the same inductors are found on all the temp sensor lines. I hope to replace them sometime soon. The best place to order them is Aliexpress you can get 200 for just $5 or so. In the mean time it's working perfectly fine and quiet.

I installed an SSD and removed the non-apple hard drive which has been installed by the previous owner and shorted pin 11 on the SATA power connector to pin 10 or 12 which are both ground and that keeps the hard drive fan at the correct speed.


Oh My.. May I just say.. Thank you.. I just soldered these two points together.. And now everything works perfekt.. I've owned this mac 3 years.. and bought it 2. hand with this error.. And just lived with it.. and now.. I just got a new Imac just by soldering!! Awesome.


I have the same problem on my imac:


So I soldered it too:


It helps me, but not for a long time - few hours it works perfectly. Then clock down to 1.6GHz and stuck on this point. But reset NVRam, reboot or sleeping mode (after awaking) helps - it became works normal for a half a day or so. But for now (about 1 week past) - helps nothing. It works on a half of clock speed.

What can be wrong? Maybe I should solder this two ferrite beads together? Or it can break something else?


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This issue, caused by Apples greed in putting proprietary drives in, can be solved easily by using this:

OWC In-line Digital Thermal Sensor for iMac 2011 Hard Drive Upgrade


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Check the LCD Thermal Sensor Cable (vertical sync cable) and the cable to your main hard drive. You didn't mention if you also changed the main hard drive or not.

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I removed the LCD panel and booted the iMac with external Cinema Display. It still behaves the same. I didn't change the main hard drive either.

I have my suspicion on the Ambient Temp. Sensor/connector, given that iMac is giving reduced performance as well as running CPU and ODD fans at max speed, which I found to be symptoms of faulty ambient sensor.

Checking TA0P (ambient sensor) value through a smc program I found, gave a value of -128C, which means no actual reading received from the sensor.

I'm, however, still open to other possibilities.


Taking the LCD panel out would make it worse, not better. Check step 8 in the guide for clarification as to what the vertical sync cable is.


The LCD temp sensor being connected incorrectly would only affect the ambient temp sensor in the iMac 2010 (and maybe 2009 too).


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I know this posting is about 8 months old, but I have to respond to mayer's comment. It's my understanding that the drives shipped with the iMac's are not proprietary at all, no custom firmware is installed. It's the cables in which they connect the HDD to the logic board that are custom. That may be a proprietary cable, but Apple is using this method to receive more accurate heat information to control the fans for better performance in reducing heat then the old way by sticking a sensor on the outside of drive.

As for a standard in how manufactures make access to the hard drives internal heat sensor is different from company to company. That is why Apple has several different cables depending on which drive is sent out in the iMac. I for one have done the upgrade to a 2 drive setup. When I purchased my iMac it was originally shipped with a Seagate drive that later was issued a recall replacement. After having the new drive installed I just assumed the swap was with an identical drive. Now performing the upgrade, it turns out the recall was replaced with another manufacturers drive including a different heat sensor cable. I didn't have the correct cable, for this upgrade. Researched on-line the pins used for the Seagate drive and modified the cable to connect properly to the heat sensor pins on the new drive.

I then installed a SSD drive and reused the sensor that was taped to the side of the SuperDrive. Slapped the iMac back together and used Time Machine to install the backup of my original drives data to the new one. When turning on the iMac for the first time after the upgrade I noticed faster loading times not fan speeds.

By making the SSD the startup drive the benefits were instantly noticeable. The iMac used to take about 45 seconds to boot up and use, now I boot up and able to use in about 10 seconds. As for the fans, they work as intended by OS X, because I modified the custom cable to get the heat data from a drive that you can pick up at any electronic store nation wide. If you're not comfortable in modifying the cable, go on-line and order the correct one for the drive being used and you will not have any problems with the fans.

So, it's not a proprietary drive or "greed" that Apple went this route, but to gain a more accurate heat reading to control the fans for better heat dissipation.

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@helliant - I'm sorry to say your half right here ;-}

The older 2009 iMac models used a standard SATA & power cable but did use a custom header cable to access the internal thermal sensor the manufactures were using for testing during the drives burn-in at the factory.

With the 2011 27" model iMac onward Apple uses a custom drive. Apple was able to get the drive makers to alter the design of the drive so they could access the sensor from within the SATA cable. They did go to the JEDEC group to amend the SMART standard and also went to the EIA/SATA group to amend the SATA standard. From what I've been told the JEDEC did their part the EIA didn't, so drives are unique to Apple.


Apple also went their own way with the M.2 blade SSD interface as they wanted to use their own custom firmware on the SSD's to push the limits of the SSD which at the start was using a mSATA config. Later on with the release of the PCI version of MacBook Pro's & Air's they again went their own way!

While the physical design the blade SSD as well as the PCIe signaling its self is within the M.2 spec, the layout of the pins and the pin signal alignment are not compatible with more common M.2 standard config. Which is why some people have managed to create adapters to host the Apple SSD's in other PC's or even create an adapter to allow someone to use a M.2 SSD in a PCIe version of MacBook system (what is not said here is the SSD is running in mSATA mode not PCIe mode).

It also appears Apple implemented a 4 lane (4x) PCIe interface in the first generation of PCIe systems but only put in 2x SSD's. If that is true people with older PCIe models may want to look at getting a newer 4x SSD's if they are upgrading.


Hi there, and thanks for the reply! I would like to know if my iMac has the 4x PCIe, iMac (27-inch, Late-2009) 11,1 and the Intel i7 2.8GHz upgrade. When I bought the SSD, I made sure not to spend the extra amount for a faster 6 Gbps drive and only got the 3 Gbps one. Because I was led to believe the systems limitations was just that. Anyway, thanks for kicking me in the pants and setting me straight, knowledge is power! Anyway, if you know that I indeed do have a faster bus speed, let me know?


@helliant1 - Sorry for not catching this sooner, your systems drive interface is strictly SATA running 3.0 Gb/s (SATA II) It does not have an exposed PCIe bus.


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I had an interesting endeavor with a Mid 2011 iMac 27”. I wanted to replace the broken harddrive with a new 2,5” one and add an SSD on top of it. I got the cable for the second drive and was able get everything up and running - except that the fans were running at full speed shortly after switching the iMac on.

The first thing I came across was the issue with the non-standard HDD temperature reporting. I stumbled upon https://www.elvikom.pl/imac-21-5-27-blad... which describes that you can shorten two pins on the harddrive to let the iMac think temperature is normal. I did this on a Sabrent converter frame (3,5” to 2,5”) to avoid soldering directly on the harddrive. Guess what? Fans still spinning at full speed.

Then I tried the OWC OWCDIDIMacHDD11 which is similar to the solution offered by iFixit to add an external temperature sensor for the HDD. Aaaand it was still not working. Fans at full speed.

I was a bit out of ideas. Some weeks later I gave it another try. The whole time I was running the iMac with the display removed to make things easier while in repair. I had it connected to an external display. I ran the Apple Hardware Test and it showed me this error: 4SNS/1/C0000008: TL0P—124. I found out that this is a problem with the display temperature sensors. And indeed they were not shown by Macs Fan Control.

Obviously, this was due to the fact that I didn’t have the display attached, However, even after attaching it I got the same error and fans spinning at full speed. I removed the display again and found the temperature sensor on its backside. I removed its connectors and re-attached them. Then I attached the display again and tried starting the iMac without the additional OWC cable (i.e., only with the soldering solution). And it worked! Fans were quiet and I could see the display temperature sensors being shown by Macs Fan Control.

In the end, it seemed to be a problem with connectors of the display temperature sensor. So the iMac didn’t recognize them and turned on the fans. What a ride.

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