10 Replies Latest reply: May 3, 2010 2:34 AM by MacSpiller
MacSpiller Level 1 (0 points)
Hi Mac Users,

Could someone please inform me what is GPU Diode?

On the istat nano temp range, it sates that its at -127 degrees? (computer has been on for an hour, just web surfing).

My MBP is just a day old & I never saw these sort of temp ranges on my previous MBP core2.


MacBook Pro 15" i5 2.4ghz, Mac OS X (10.6.3)
  • eww Level 9 (52,975 points)
    Fahrenheit or Celsius?
  • MacSpiller Level 1 (0 points)
    Sorry should have mentioned its Celsius.....
  • eww Level 9 (52,975 points)
    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?
  • MacSpiller Level 1 (0 points)
    yes, its reporting a minus 127"C. The machine doesn't feel hot at all nor am I doing anything intense.

    I have the latest Istat Nano. I downloaded it yesterday, and did not see this reading until today.

    The strange thing though is that every other temp indicators are changing except for the GPU Diode which is still staying on at minus 127 celsius. My computer has been on now for 3hrs and both fans are not exceeding more than 2003rpm.

    Have you ever seen a reading like this before? & what might that indicate?
  • Retired Engineer Level 4 (2,735 points)
    That is an invalid reading. Water freezes at 0 degrees C. 127 degrees below zero (-127) is not possible.
  • Rod Hagen Level 7 (31,985 points)
    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.


  • eww Level 9 (52,975 points)
    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.
  • MacSpiller Level 1 (0 points)
    Not sure what is going on....GPU Diode now doesn't exist? It just says GPU which is at normal range of 30"C.

    Well I guess if I don't see that reading again I wont need to bother. However, I do believe there might have been a fault or error at that time with the readings. If it happens again will run a hardware test & post back any error codes.

    Thanks heaps for all your input/time

  • Rod Hagen Level 7 (31,985 points)
    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.


  • MacSpiller Level 1 (0 points)
    Thanks for that Rod.

    I now believe it is definitely related to the switching of the integrated graphics card between the GeForce 9400M and the GeForce GT.

    Phew....I was worried for a second. And you are right, the current iStat Nano does not support the switching graphics. Thank you for the links....will check out Cody's app & see what readings I get.