Fans Constantly on

Discussion in 'MacBook Pro' started by JPT, Apr 14, 2010.

  1. JPT macrumors regular

    May 4, 2006
    So today I opened up my MBP to clean it out and stuff (it had a ton of dust... A wall of it had built up where the fans blow out)

    All is fine and dandy now except for one thing. Since I don't want to open my case up for the second time today (right fan wasn't plugged in all the way first time I started it up... oops x( ) I'm asking here since everything else seems to be fine.

    What I did:
    Opened everything up all the way down to the heatsink.
    Applied correct amount of Thermal paste.
    plugged everything back in (right fan wasn't perfect at first, but fixed and stupidly didn't double check everything else while I was in there)

    And now both fans are running at 6k (full) constantly. I tried resetting PRAM and SMC with no luck. I'm about to grab my disk 1 and run the diagnosis to see if that turns up anything.

    Are there any plugs that I might have accidentally not plugged in all the way or at all that would cause this? Also any other suggestions if everything is plugged in correctly?

    MacBook Pro 2,2 15.4" late '06
    C2D 2.33GHz
    2GB Ram

    Also, I have iStat Menu. No apps using all my CPU (Mostly <10% usage right now) and temp is mostly <40c right now. All temps have a temperature so I'm assuming all heat sensors are fine.

    On a great note: My computer is so much cooler now! Even before this at 6k rpm I'd get down to MAYBE 45c if I was lucky.

    Edit: I also have Fan Control installed and it's not having any effect :(
  2. Pax macrumors 6502a

    Dec 12, 2003
    Most likely a bad sensor. Hopefully you forgot to plug it back in. There are some sensors which iStat doesn't report. In particular there are some on the heatsinks near the fans which iStat doesn't see.

    It seems that if the SMC fails to get a valid reading from any sensor, it puts the fans into fail safe max speed mode.

    If you run Hardware Test it will show you which sensor has failed. In older versions of HT it just gave a cryptic code eg "Th0h" but I believe that in the latest versions it gives descriptive info as well.

    The trick then is to find out which sensor it is that's gone bad. I got as far as decoding some of them

    Th is for thermal sensor
    0 is a digit, there are usually 3-4 covering one area
    h = heatsink; d = die; p = proximity (enclosure I think). There may be more

    If you get stuck you'll have to unplug sensors one after another and run HT after each one until you find the dud.

    There was a thread on this a couple of weeks ago - I can find it but it didn't contain much more info than this.

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