I recently replaced the logic board on my Mac, now I have this "fan constantly on at 6000RPM all the time" issue.

So I did an Apple hardware test using the installation disk that came with my Mac and got this cryptic error: 4SNS/1/40000000:Th2H-128.000

After some googleing I came across this:

Th2H Right Fin Stack Proximity Temp

And my question(s), what part does the Right Fin Stack Proximity Temp refer to?

Is the error given by the Apple Hardware Test considered 100% accurately?

2 Answers 2


This is a guess but I would assume it's referring to the Temperature sensor next to the heat sink exhaust for the right fan. That would definitely account for your fan running at max... if the sensor is not reporting the temperature, the logic board would likely turn the fan on full blast in order to keep the processor from overheating or even setting the computer aflame.

You might have just forgot to plug the temp sensor in, or left it loose, or it became loose during your board replacement. Or it could have failed...

Try using a temperature monitoring app like Temperature Monitor and see if it gives you any more info.

  • I was quite pedantic during assembly, though humans are full of error. Here's a report saved from Temperature Monitor: bit.ly/c0ty1F There's no mention of any right fan sensor, should there be?
    – timduffin
    Nov 9, 2010 at 9:34
  • what model MBP do you have? Nov 9, 2010 at 15:17
  • if we knew that, maybe someone with a similar model could post their sensor report as well and we could see if there is any difference... mine is too different to be of any use i think: pastebin.com/UyB6aPQQ Nov 9, 2010 at 15:38
  • also, in the temperature monitor temp readings, does it show readings for both of your cpu cores? Nov 9, 2010 at 16:02
  • Calavera, The model: MacBook Pro 15" Core 2 Duo A1260 (early 2008) - In Temperature Monitor, variable reading are show for all the sensors here: pastedump.com/paste/1107 Thanks.
    – timduffin
    Nov 11, 2010 at 9:27

The best solution is to use the app Macs Fan Control (Free), and setting it to control the fans using the GPU (or whatever sensor usually shows the highest temperature) instead of the malfunctioning sensor.

During start, the fans will run high, but when Macs Fan Control kicks in, the fans runs exactly how you want them run.

Download from http://www.crystalidea.com/macs-fan-control

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