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Model A1286. Released February 2011 / 2.0, 2.2, or 2.3 GHz Quad-core Intel Core i7 Processor

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How to Disable/Swap faulty Temperature Sensor?

Hey there!

My 3,5 year old MacBook (OSX 10.9.1) stopped working last week.

After watching some videos on youtube the screen just turned gray and all I could do was to force it to shut down.

When I start the device now the screen shows briefly the Apple Logo and then I get the same gray screen.

I tried SMC and PRAM reset, booting in save and recovery mode etc. but I can't launch the OS. All I get is a gray screen. (in save mode it is black)

Only the hardware test worked. It showed this error code after the test:

4SNS/1/C0000008: TsOP--124

After some research I found out, that this refers to a faulty temperature sensor.

So I have 2 questions:

Can you tell which sensor it is and if I can replace or fix it, OR disable it in software?

Could it be, that the problem is not caused by the faulty heat sensor but something else? Because from what I have read so far, faulty heat sensors usually cause high fan speeds and no gray start screen.

PS: sorry for bad grammar or misspellings, english is not my mother tongue.

Answered! View the answer I have this problem too

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Here's a good writeup on how to decode Apple Hardware Test error codes: CNET - How to invoke and interpret the Apple hardware tests

Looking at your error: 4SNS/1/C0000008: TsOP--124

4SNS: System sensor

T: Temperature

s: Palm rests for laptops

O: Optical drives

P: Power bus

You have a few sensors firing off here ;-{ Lets see if you can isolate this down a bit.

Lets try restarting under Safe Boot mode. Follow this Apple TN" OS X: What is Safe Boot, Safe Mode?. Does the system appear to run longer without into a grey screen? If it does from another Mac system download this Temperature Gauge Pro and copy it over to your system and install it. It should help show you what your sensors are telling you. You may need to stick your system into a tight plastic bag (taking as much air out as possible) in your refrigerator for a few hours (not to long and don't freeze it!).

I suspect your heat sink has failed. The clue will be seeing all of the heat sensors running high and your fans running at full speed.

Paste in a screen shot or two so we can see the sensors of Temperature Gauge Pro.


OK, the screen shot of Temperature Gauge shows the fans are not working at all. Thats not good. Do you hear them? If you do the sensor on the fan units are not registering within SMC. So the SMC is not controlling them.

The screen shot of the display shows us the GPU is failing likely from the heat if the fans are not working correctly.

The function of cooling the system was to buy some time if the system didn't run very long. At this point I don't think it offers anything useful.

You stated you got the system back from service what did they do? And what was the reason you brought it in?


Just to be clear here, a defective temp sensor would not cause your display to react like it has.

Looking at Temperature Gauge shows us all of the temp sensors are working! So there is nothing here to replace on the sensors them selves.

The only sensor that appears not working is the tach's for the fans, they don't appear to be running high enough (better than 2k RPM) given the heat levels. If they are working and the screen shot is not telling me correctly then the GPU chip is failing here. You'll need to get the full version so you can track the temp & fan condition when the screen goes on you to verify this.

So far I don't see replacing the heat sink (or redoing the thermal paste) is the answer until we can deal with the fan issue. You are sure the system has not gotten wet some how? Correct

If the fans do ramp up as the system gets warmer and the temp of the GPU does not go red line then the GPU chip it's self has a problem.

It could be a cold solder joint or a defective chip. Other than swapping out the logic board there is not much one can do here with a BGA chip setup with out the proper gear.

You may want to get your system to a Apple Store as they check to see if there was a recall for this unit and they often offer a cheaper price for logic board swap outs.

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Hey Dan,

thank you for your answer, especially the explanation of the error code!

I tried to do what you wrote, so I started the MacBook first time again since I've got it checked from a reseller and... MIRACLE! I was able to boot the OS!

No gray screen after the Apple logo, just my desktop and everything seemed to work fine. I thought the reseller must have fixed it without telling me, but they said they didn't?!

So I installed Temperature Gauge and made a Screenshot:

At that moment the system was in idle, so I started a video on youtube to check the temperature again.

After 6 seconds the picture froze and it looked a little bit like that:

(I forgot to take a photo of it)

So I had to force shut down the MacBook. When I tried to restart the OS did not boot and I got the gray screen again.

So I tried to boot up in Safe Boot mode, but after loading for a while the screen turned black and was unresponsive.


During all this the fans never ran fast.

Should I try to put the MacBook in the fridge now to do some more tests or do you have an idea what to do?

PS: why is the comment-system ignoring breaks?


Yes, the comment section doesn't have line breaks. The thought I think was to limit the comments to a single thought. Which does create problems when you need to make a statement more so than a simple thought.


Just so you know I have no affiliation with the company but you might want to get the full version here as the full version has logging which is quite useful on problems like this. It's still the best tool I've found to monitor things.


The Fans are working, I can hear them. They also run faster when I am doing a Hardware Test, for example.

I brought the MacBook to a reseller because of the problem we are trying to solve right now. They said they did not do anything but a hardware test and checking the internals. They told me the sensors are failing and all they could do is change the logic board for 1200€ (=1600$).

Do you think changing the heat sink could help? Because I don't think that the sensors are not working, because they seem(ed) to work fine in temperature gauge.


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I have the same problem but updating the BIOS didnt work. Please help me, as my fan runs automatically always and 90B error is displayed always at startup, from the very first day I bought HP Probook 4430s. Even the vents are clean and I regularly clean them. Still it shows the same error. I have also replaced the fan but still it shows the same error.

Please suggest me what can be the reason and what can be a possible solution.

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@rishabhrocks2000 - This question is on the Apple's MacBook Pro 15" system. You'll need to create your own question with all of your details. While it may appear to be the same problem the hardware design is very different on the HP to the Apple systems.


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I have had the same issues along with a few others with my 15' Early 2011 MacBook Pro. Check out this website.

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@ckapplei - It's one thing to aim someone to an Apple note for the subject. But, in this case the issue is a thermal sensor not a display/graphics issue. So why are you posting this?


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creezebert will be eternally grateful.
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