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2.2 GHz (Turbo Boost up to 3.4 GHz) or 2.5 GHz (Turbo Boost up to 3.7 GHz) quad-core Intel Core i7 processor with 6MB shared L3 cache.

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MBP Retina 2014 CPU overheating due to temp sensor bug

So in this client’s MBP CPU apparently has a bug in temp sensor which leads to incorrect temperature reporting and overheating leading to kernel panic eventually.

While in OS it can be alleviated by tool like SMCFanControl by just ramping up fan speed regardless of reported temps but it is not working during preboot such as system updates leading to overheating and KP because fans are spinning too low(since SMC getting wrong temp) for generated heat. And KP during updates means hello to system reinstall (which by itself can only be successfully done if room ambient temperature is around zero in Celsius). Which is no fun.

So I am thinking about cheap & cheerful way of going around problem since replacing CPU is not very cheap in my book.

What do you guys know about manual changing fan speed due to resistance on some of fan lines? What are on fan connector pins in this MBP? Could it be that adding simple hardware switch like shorting one pin to ground will put fan in full blast? If that can be done so that would be just enough for the moment of installing system update and anything else can be fixed on OS level.

Any ideas appreciated!

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Lets get a better idea on whats happening here. Disable SMCFanControl and instead install this app: TG Pro. Post a snapshot of the main window (you may need to resize the bottom so we can see all of the sensors) Adding images to an existing question

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I’ve not encountered a CPU thermal sensor failure (sensor within the CPU).

I’ve seen lots of sensor issues due to corrosion damage around the SMC chip (which on this system is on the backside of the logic board) and other locations on the logic board. As well as dust buildup or fan failure.

What often happens is the owner had a liquid spill into the keyboard and/or trackpad and the liquid dripped down onto the logic board and was not cleaned so over time things go from bad to worse!

I would recommend you pop the logic board out and take some good detailed pictures of the board both sides and post them here so we can locate whats damaged.

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Thank you for a suggestion, Dan. No corrosion on SMC or around it. All leads to CPU temp sensor is way off. CPU doesn't throttle for example. So idea is to do some hack here.

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Iskra - Can we get the TG Pro output so we can make sure you're facing a real issue within the CPU.

In all my years fixing systems I've yet to see the built-in CPU sensor fail.

You may want to look at Activity Monitor to see whats happening within it. Is any process consuming too much?

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I'll try to provide that later. Now it is at my fellow repair guy who is unlike me and is good with oscilloscope and schematics.

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iskra will be eternally grateful.
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