GPU Diode -127deg??

Fahrenheit or Celsius?

I should also have asked whether it is actually reporting minus 127°C, as you indicate, or plus 127°C?

If it's reporting a negative temperature for anything, there's a real problem. Is the machine extremely hot? Are you sure you're using the latest version of iStat Nano?

That is an invalid reading. Water freezes at 0 degrees C. 127 degrees below zero (-127) is not possible.

The most likely explanation is that the version of iStat that you are using has not been updated for the latest MBPs, I would think.

Another possibility may be that this is a 'default" or "error" value that the program uses if no real information is available. This might occur if, for example, the discrete GPU is not actually "on line" at the time.

Cheers

Rod

Another possibility is that your MBP's GPU diode temperature sensor is faulty. Run the Apple Hardware Test that you'll find on one of the discs that were shipped with the MBP. If it reports any errors, post back with the exact text of the report. Any error code that contains SENS is likely to be confirmation of a bad sensor.

In another thread here it looks pretty clear that this issue is occurring in those situations where the NVidia card is simply shut down and the computer is running on integrated graphics, MacSpiller.

No doubt iStat will be updated to accommodate the switching graphics machines before too long (if it hasn't already)


Another more comprehensive monitoring program, "Hardware Monitor" in such situations, simply identifies the same sensor as "disconnected". Its author, Marcel Bresink , explains such situations as follows at http://www.bresink.com/osx/216202/issues.html, after having pointed out earlier that some other monitoring software gives spurious results when sensors are not actually available:

+In this case, you must be using a Mac capable of switching between two alternative graphics solutions, for example a pair of an Nvidia GeForce 9400M and a GeForce 9600M GT, or Intel HD Graphics paired with an Nvidia GeForce GT 330M. It is the correct and expected behavior to only show the sensors which are currently online. The sensors of the GPU which is currently offline are powered down and even cannot be detected.+

If you run iStat alongside Cody's useful little app for deciding which Graphics are in use ( http://codykrieger.com/gfxCardStatus/ ) and compare your GPU results with the temperature figures then it should be easy enough to see if this is the cause of the strange number you are receiving.

Cheers

Rod