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kernel_task error + faulty temperature sensor

I woke my 2013 MacBook Air from sleep mode to discover it running extremely slow with the fans blasting. I opened the Activity Monitor and discovered the system's kernel_task using essentially all of the machine's CPU resources.

I attempted to follow all of Apple's recommended solutions (reset SMC, PRAM, reinstall OS, etc.) before following some instructions I found online to tamp down the kernel_task process by altering a few files in the OS. After that, I successfully regained control of the machine (although the fans were still blasting) and was able to run a hardware diagnostic.

I got the following error code: 4sns/1/c0000008 th1h -- 124.

According to a Google search and this forum, that means I have a faulty temperature sensor. I downloaded a temperature monitor/fan control program that claims while my battery/palm rest sensors are ~75 degrees F, my CPU is 107-130 degrees F. The computer does not even feel warm to the touch.

This is an older machine, and I'm a graduate student, so I'm not going to put $400 into a new logic board. Now that I can control the fans, the machine seems to be operating just fine. Accordingly, I'm curious about my options.

1. Am I right to assume that these CPU temperatures as reported by that sensor are false positives and that those components are not actually running at unsafe temperatures?

2. Is it worth it to open up the machine and blast it with compressed air?

Many thanks!

UPDATE: Screenshots from fan control app and a hardware monitor

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Those two temperatures that you specified are definitely in range and working properly, since 75F is around room temperature and therefore accurate for the palmrest, and even 130F is totally normal for the CPU. However, you definitely do have a temperature sensor error somewhere else, as there are many sensors in your laptop. If you have a temperature monitoring app and post a screenshot of the thermal sensor readouts, then we may be able to isolate the affected part inside your computer. Alternatively, if you are able to download and run ASD OS 3S150, then it will clearly specify the faulty sensor(s).

kernel_task is the mac responding to a out-of-spec readout from a sensor, and is a way in which the mac executes low-overhead tasks to the CPU in order to reduce the load on the CPU, and ensure the the CPU doesn't not overheat. It also causes the fans to spin at 6000rpm.

As the majority of the sensors are located inside the logic board, you will most likely need to get the board replaced or repair it, but there is also a possibility that the faulty sensor is located in a peripheral device such as the trackpad, which would only require you to replace that part.

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4 Comments:

Hi Sam,

Thank you so much for your response. I updated the question with two screenshots - one from the fan control app and one from a hardware monitor (taken about 15 minutes later). Unfortunately, I couldn't figure out how to align the units.

Given the age of the machine, I don't think I can justify the cost of a full logic board replacement. Accordingly, I'm interested in my other options, including what I can do without doing any hardware work at all.

Thanks again!

-Dan

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It's unfortunately hard to tell which sensor is the issue from those screenshots - if you try to run the laptop from the magsafe charger with the battery unplugged, does the issue persist?

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Unfortunately, the battery isn't removable on this device

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You just need a Torx T5 and pentalobe screwdriver, and a couple minutes :) MacBook Air 13" Mid 2012 Battery Replacement

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Dan Greenberg will be eternally grateful.
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